Breast Cancer: Symptoms, Stages, and Treatment
In this article
What Is Breast Cancer?
Breast cancer is a disease that develops when cells in the milk ducts or milk-producing glands (lobules) of the breast tissue multiply uncontrollably. It is the most common cancer among women worldwide, and treatment success is very high when it is detected at an early stage. In this guide, we discuss in detail the causes of breast cancer, diagnostic methods, the current AJCC 8th edition staging system, and personalized, step-by-step treatment approaches according to molecular subtype (hormone receptor/HER2 status).
Breast cancer is not a single disease but a collective term for several subtypes with different biological behavior and different treatment requirements. The current approach therefore relies not only on tumor size and spread but also on hormone receptor (ER/PR) status, HER2 status, and tumor grade — this information determines both prognosis and which drugs will be effective.
Breast Anatomy
The breast is a complex organ consisting of glands responsible for milk production (lobules), ducts carrying the milk to the nipple, the surrounding fat and supporting tissue, and lymphatic circulation. The vast majority of breast cancers begin in the milk ducts (ductal carcinoma) or, less commonly, in the lobules (lobular carcinoma).
The chest muscles (pectoral muscles) lie beneath the breast tissue; although cancer is directly adjacent to these muscles, it has no direct relationship with them and is assessed separately under the T4a category in staging. The lymphatic network around the breast drains particularly to the axillary (underarm) lymph nodes and internal mammary lymph nodes behind the breastbone — these nodes play a key role in assessing the regional spread of cancer.
Breast tissue is sensitive to estrogen and progesterone; these hormones directly affect its structure during puberty, pregnancy, breastfeeding, and menopause. The same sensitivity underlies the need for these hormones to support growth in some breast cancer cells (hormone receptor-positive tumors).
How Common Is Breast Cancer? (Current Statistics)
According to the International Agency for Research on Cancer (IARC) report "Global cancer statistics 2024" (Sung H, et al., CA: A Cancer Journal for Clinicians, published on 8 July 2026, DOI: 10.3322/caac.70090), the 2024 data indicate that approximately 2.434.087 new breast cancer cases (11,8% of all cancers) and 693.660 deaths from breast cancer were reported. Among women, breast cancer ranks first for both incidence and cancer-related deaths (ranked 1st for incidence in 164 countries and for deaths in 122 countries). Incidence in countries with a high level of development (approximately 54/100.000) is significantly higher than in countries with a low-to-middle level of development (approximately 34/100.000) — this difference is also associated with the availability of screening programs and diagnostic capacity.
According to the American Cancer Society report "Cancer Statistics, 2026" (Siegel RL, et al., CA: A Cancer Journal for Clinicians, published on 13 January 2026, DOI: 10.3322/caac.70043), approximately the following are expected among women in the United States in 2026: 321.910 new invasive breast cancers and 60.730 new DCIS (in situ) cases ; the estimated number of deaths is 42.140. During 2013-2022, incidence increased by an average of 1% annually, with a more pronounced increase of 1,4% per year in women under 50 . Meanwhile, from its peak in 1989 through 2023, the death rate decreased by 44%, meaning approximately 546.000 deaths were prevented — however, the pace of this decline in recent years (approximately 1% per year since 2010) has slowed compared with the 2000s (approximately 2% per year). 5-year relative survival by stage is over 99% in localized disease, 87% with regional spread, and 32% with distant metastases; it is 92% for all stages combined (cancer.org, 23 July 2026 update, SEER 2015-2021 diagnosis cohort). The lifetime risk of breast cancer is approximately 1 in 8 women (~13%).
According to the GLOBOCAN 2024 country profile for Türkiye, approximately 25.080 new breast cancer cases are reported annually in Türkiye, putting breast cancer in 1st place among cancers in women (approximately 24,5% of female cancers); the age-standardized incidence rate is 44,2 per 100.000. Annual deaths number approximately 5.613, and the age-standardized mortality rate is 9,1 per 100.000. According to reviews by Turkish breast surgery specialists based on national registry data, the average age at breast cancer diagnosis in Türkiye is approximately 51,6 , with 17,1% of cases diagnosed under the age of 40 — a significantly younger age distribution than in Western countries (some press statements also describe this difference as "approximately 10 years younger than the world average"). According to the same review, approximately 75% of patients are diagnosed at an early stage (Stage I-II), and 70% are hormone receptor-positive.
Risk Factors
Having a risk factor does not mean that you will develop breast cancer; similarly, having no risk factors does not guarantee that cancer will not develop. Risk factors are influences that increase or decrease the likelihood.
General Risk Factors
- Female sex and increasing age
- History of breast cancer in a first-degree relative
- Inherited mutation in BRCA1/2 or other genes
- Early onset of menstruation (<12 years) or late menopause (>55 years)
- Never giving birth or having the first birth after age 30
- Dense breast tissue
- History of atypical hyperplasia
- Exposure to ionizing radiation in the chest area
- Postmenopausal obesity
- Regular alcohol consumption
- Long-term combined hormone replacement therapy
- Physical inactivity
Inherited (Genetic) Risk: BRCA1/2 and Other Genes
Approximately 5-10% of breast cancers are due to an inherited gene mutation. The most common genes associated with the highest risk are BRCA1 and BRCA2, but many more genes are now screened together in routine genetic panels:
| Gene | Associated Syndrome | NCCN Risk Category | Lifetime Breast Cancer Risk |
|---|---|---|---|
| BRCA1 | Hereditary breast/ovarian cancer | High | %60-72 |
| BRCA2 | Hereditary breast/ovarian cancer | High | %55-69 |
| PALB2 | — | High | %32-53 |
| PTEN | Cowden syndrome | High | 85-91% (penetrance by age 50 ~50%) |
| TP53 | Li-Fraumeni syndrome | High | Rather than a separate breast-specific rate, the total cancer risk in female carriers can reach ~90% by age 60; breast cancer is the dominant component of this risk |
| CDH1 | Hereditary diffuse gastric cancer / lobular breast cancer | High | 37-55% (predominantly lobular type) |
| ATM | — | Moderate | %21-24 |
| CHEK2 | — | Moderate | %23-27 |
| STK11 | Peutz-Jeghers syndrome | High (generally accepted) | Significantly increased (a genetic counselor should be consulted for the precise isolated breast-specific NCCN rate) |
For comparison, the general population risk is approximately 13% (1 in 8 women). Source: NCCN Genetic/Familial High-Risk Assessment Guideline (Version 2.2026) and NCI BRCA Fact Sheet (19 July 2024 update).
Genetic testing criteria have expanded significantly in recent years. According to the joint guideline from ASCO and the Society of Surgical Oncology (SSO), published on 4 January 2024 (Bedrosian I, et al., Journal of Clinical Oncology, DOI: 10.1200/JCO.23.02225), almost all patients newly diagnosed with breast cancer at age 65 or younger (Stage I-III or de novo Stage IV) should be offered germline genetic testing — a major expansion beyond narrower traditional criteria such as "under 45" or "triple-negative and under 60." For those diagnosed over age 65, testing is still recommended in the following circumstances: disease eligible for PARP inhibitor treatment, triple-negative breast cancer, suggestive family history, male sex, or founder-population ancestry such as Ashkenazi Jewish ancestry (no age limit applies in this last group).
Breast Density (Dense Breasts)
Breast tissue that appears dense on mammography — containing more glandular and fibrous tissue relative to fat — both increases breast cancer risk and reduces mammography's sensitivity for detecting tumors. Risk increases progressively with density categories (from BI-RADS A to D); in the densest category (BI-RADS D), risk is approximately 4 times greater than in the least dense category. Women with dense breasts should therefore discuss with their physicians whether additional imaging (ultrasound or MRI) is needed.
Hormonal and Reproductive Factors
Early onset of menstruation, late menopause, never giving birth, or having the first birth at an older age slightly increase risk by extending estrogen exposure; breastfeeding is thought to have a protective effect. Long-term (more than 5 years) combined (estrogen+progestin) hormone replacement therapy may increase risk; however, this area is being actively reassessed — for example, new data presented at the 2025 San Antonio Breast Cancer Symposium suggested that hormone therapy (particularly estrogen-only replacement) after risk-reducing ovarian/fallopian tube surgery in BRCA1/2 carriers does not increase breast cancer risk and may even be protective — but this finding applies only to BRCA carriers whose ovaries/fallopian tubes have been removed and must not be generalized to the overall population. There is a dose-dependent relationship between alcohol consumption and breast cancer risk; according to the ACS 2026 report, approximately 16% of breast cancer cases in the United States are attributed to alcohol consumption and 7% to physical inactivity. Postmenopausal obesity also increases risk because of the role of fat tissue in estrogen production.
Symptoms
- A new lump or thickening in the breast
- A change in the breast's size or shape
- Skin dimpling or an orange-peel appearance
- An inverted nipple
- Redness, scaling, or rash on the nipple
- Nipple discharge (particularly bloody)
- Swelling or a lump in the armpit
- Persistent breast pain
- Skin redness or increased warmth
Many of these symptoms may be due to benign causes (cysts, fibroadenomas, infection); however, a physician should be consulted without delay if any are noticed. Swelling in the armpit or around the collarbone may indicate lymph node involvement; persistent bone pain may indicate bone metastasis; and a continuing cough or shortness of breath may indicate lung metastasis — these symptoms do not directly mean metastasis but must be assessed. Rapidly developing widespread skin redness, increased warmth, and an orange-peel appearance are typical signs requiring urgent assessment of inflammatory breast cancer and may often appear without an obvious lump.
How Is It Diagnosed?
Clinical Examination and Imaging
The diagnostic process starts with a clinical examination, followed by imaging methods. Mammography is the primary method for detecting early breast cancer. Ultrasound is used to distinguish a solid mass from a fluid-filled cyst and to assess axillary lymph nodes. Magnetic resonance imaging (MRI) is not used routinely but is preferred for BRCA mutation carriers, people with a strong family history, those diagnosed with lobular cancer, or when mammography/ultrasound is insufficient; it may also be used to assess response to neoadjuvant treatment.
Biopsy
A biopsy must be taken from the suspicious mass before treatment is planned. The most commonly used method collects a tissue sample with a needle under ultrasound guidance (mammography or MRI if needed): Tru-cut (core needle) biopsy. A biopsy provides the tissue needed to determine the tumor's histological type, grade, and hormone receptor/HER2 status; this information forms the basis of the treatment plan.
Sentinel Lymph Node Biopsy
Assessing lymph node involvement is a critical part of staging. In patients without clinically detected lymph node involvement, a radioactive tracer and/or dye is injected into or around the tumor to identify the first lymph nodes cancer cells would reach (sentinel lymph nodes), and only these nodes are removed and examined — this prevents unnecessary removal of all axillary lymph nodes (and the associated risk of lymphedema).
Molecular Subtypes: Hormone Receptor and HER2 Status
Today, three biological features of the tumor determine the foundation of breast cancer treatment: estrogen receptor (ER) / progesterone receptor (PR) status, HER2 status, and histological grade. These three features are assessed in biopsy tissue using immunohistochemistry (IHC) and, when needed, in situ hybridization (ISH/FISH), placing the tumor in one of four main subgroups:
| Subtype | Definition | Approximate Frequency |
|---|---|---|
| Hormone Receptor-Positive, HER2-Negative | ER and/or PR positive, HER2 negative | The most common subtype, approximately 70% of all cases |
| HER2-Positive | HER2 overexpressed (IHC 3+ or ISH amplified), variable hormone receptor status | ~%15-20 |
| Triple-Negative (TNBC) | ER, PR, and HER2 all negative | ~%10-15 |
Traditionally, HER2 status was classified as either "positive" or "negative." However, with the development of HER2-targeting antibody-drug conjugates such as trastuzumab deruxtecan, it became clear that some tumors previously considered "HER2-negative" actually express low levels of HER2 and can benefit from these drugs. HER2-low is defined as IHC 1+ (any staining) or IHC 2+ with ISH-negative status (confirmed by the DESTINY-Breast04 study); HER2-ultralow is a more subtle category reported as IHC 0 but showing faint, incomplete membrane staining in ≤10% of tumor cells (thus distinct from genuinely "zero" staining), defined by the DESTINY-Breast06 study. This distinction is discussed in detail in the metastatic treatment section below.
Staging: The TNM System (AJCC 8th Edition)
Breast cancer staging is based on the TNM system, consisting of the T category describing tumor size, the N category describing lymph node involvement, and the M category describing distant metastasis. The most important innovation introduced by the AJCC 8th edition (2018), alongside traditional staging based solely on anatomical spread, was defining a system that also considers tumor grade and hormone receptor/HER2 status: the "prognostic stage" system — both are discussed below.
T Category: Tumor Size
| T Category | Definition |
|---|---|
| Tis | DCIS (ductal carcinoma in situ) or Paget disease (without a mass) |
| T1mi | Microinvasion, ≤1 mm |
| T1a / T1b / T1c | >1-5mm / >5-10mm / >10-20mm |
| T2 | >20-50mm |
| T3 | >50mm |
| T4a | Spread to the chest wall |
| T4b | Skin ulceration/edema (orange-peel appearance) or satellite nodules |
| T4c | T4a + T4b together |
| T4d | Inflammatory breast cancer |
N Category: Lymph Node Involvement
| N Category | Definition |
|---|---|
| N0 | No lymph node involvement (if isolated tumor cells ≤0,2mm or ≤200 cells are present, this is separately indicated as pN0(i+)) |
| N1mi | Micrometastasis: >0,2mm/>200 cells, ≤2,0mm |
| N1a | 1-3 axillary lymph nodes |
| N1b | Internal mammary lymph node (detected only by sentinel biopsy, not clinically apparent) |
| N1c | N1a + N1b together |
| N2a | 4-9 axillary lymph nodes |
| N2b | Clinically detected internal mammary involvement without axillary involvement |
| N3a | ≥10 axillary lymph nodes or infraclavicular involvement |
| N3b | Internal mammary + axillary involvement together |
| N3c | Supraclavicular lymph node involvement |
M Category
M0: no distant metastases. cM0(i+): no clinical/radiological evidence of metastases, but tumor cells ≤0,2mm detected in blood/bone marrow/other tissues. M1: distant metastases confirmed by imaging or biopsy.
Anatomical Stage Groups (Stage 0 - IV)
Anatomical staging based solely on the T/N/M combination is illustrated in the images below (these reflect conventional anatomical staging; the current prognostic stage may move this stage down or up depending on tumor biology — see the note box below):
The most important difference in the AJCC 8th edition is the "prognostic stage group," which adjusts the anatomical stage according to Nottingham histological grade and ER/PR/HER2 status (and the Oncotype DX 21-gene Recurrence Score if performed). The general principle is that unfavorable biology (high grade, hormone receptor-negative, HER2-negative — that is, triple-negative) can upstage a lower anatomical stage (for example, a small, node-negative triple-negative tumor may move from anatomical Stage IA to prognostic Stage IB); favorable biology (low grade, strongly ER/PR-positive, HER2-positive) can downstage a higher anatomical stage (for example, a low-grade, strongly hormone receptor-positive T2N0 tumor may move from anatomical Stage IIA to prognostic Stage IA). If the "prognostic stage" and "anatomical stage" in your pathology report differ, this is not an error but an expected consequence of incorporating biology into staging; it is important to discuss with your oncologist which stage applies.
Used in some patients with hormone receptor-positive, HER2-negative disease and no lymph node involvement or a limited number of involved nodes, the Oncotype DX 21-gene Recurrence Score provides additional information about the tumor's molecular behavior. In eligible patients with a score below 11, the AJCC 8th edition rule reclassifies the disease, regardless of grade or other features, as prognostic Stage IA . The precise eligibility criteria for this test (T and N category limits) should be assessed by the pathology/oncology team according to the current AJCC table.
Treatment Planning: General Approach
In nonmetastatic breast cancer (treatable with curative intent), decisions are individualized by a multidisciplinary team of a surgeon, medical oncologist, radiation oncologist, and pathologist according to the tumor's anatomical stage, molecular subtype (HR/HER2 status), and the patient's preferences. The general framework is as follows: most patients proceed directly to surgery, and pathological findings guide postoperative (adjuvant) systemic treatment; however, in HER2-positive or hormone receptor-negative/HER2-negative (triple-negative) tumors, particularly larger tumors or those with lymph node involvement, systemic treatment is preferred before surgery (neoadjuvant treatment).
Surgical Treatment
Breast-conserving surgery (lumpectomy) and mastectomy are the two main breast cancer surgical techniques. The 20-year follow-up of the NSABP B-06 study (Fisher et al., NEJM 2002) showed no difference in overall survival between lumpectomy+radiotherapy and mastectomy (approximately 46-47%, p=0,57); long-term follow-up of the Milan study confirmed the same result. Breast-conserving surgery is therefore a curative option equivalent to mastectomy in eligible patients.
Previously, every patient with a positive sentinel lymph node underwent complete axillary lymph node dissection. According to the results of the ACOSOG Z0011 study (10-year follow-up, JAMA 2017), complete axillary dissection in patients with clinical T1-T2 disease, clinically negative lymph nodes, planned lumpectomy+whole-breast radiotherapy, and only 1-2 positive nodes on sentinel biopsy can be omitted: 10-year overall survival was 86,3% with sentinel biopsy alone and 83,6% with complete dissection, with no significant difference (HR 0,85). This is an important example of de-escalation that reduces unnecessary surgical morbidity (such as lymphedema); it applies to patients who have not received neoadjuvant treatment and are not scheduled for third-field (regional nodal) radiotherapy.
Nipple-Sparing and Skin-Sparing Mastectomy
In appropriately selected patients (meeting criteria such as sufficient distance between tumor and nipple and no direct nipple involvement), preserving the breast skin or even the nipple during mastectomy can provide a better cosmetic result; these approaches are generally combined with immediate reconstruction.
Reconstruction can be performed at the time of mastectomy or later, using an implant (silicone/saline) or autologous techniques using the patient's own tissue; the choice depends on the patient's anatomy, the need for additional treatments (such as radiotherapy), and preferences.
Radiotherapy
Radiotherapy after breast-conserving surgery is standard for reducing local recurrence risk. The current standard, rather than conventional 50 Gy/25 fractions, is hypofractionated regimens (for example, 40 Gy/15 fractions, based on the START B study); the FAST-Forward study (Lancet 2020, 5-year follow-up) showed that a regimen completed in only 1 week, 26 Gy/5 fractions , was also equivalent to 40 Gy/15 fractions for local control (5-year local recurrence: 1,4% vs 2,1%), and this shorter regimen has entered clinical practice. Postmastectomy radiotherapy is standard with 4 or more positive lymph nodes; with 1-3 positive nodes, it is assessed according to high-risk features. Partial breast irradiation (irradiating only the tumor bed) may also be an option for selected low-risk tumors (small, node-negative, hormone receptor-positive).
Systemic Treatment in Early and Locally Advanced Breast Cancer (by Subtype)
Hormone Receptor-Positive, HER2-Negative
Standard adjuvant treatment continues for 5-10 years with tamoxifen or aromatase inhibitors (anastrozole, letrozole, exemestane), depending on menopausal status. Adding ovarian function suppression provides additional benefit in high-risk premenopausal patients, particularly younger patients (<35 years) who have received chemotherapy: according to the combined analysis of the SOFT/TEXT studies (NEJM 2018, 2022 update), in this high-risk group, 8-year disease-free survival was 71% with tamoxifen alone, 76,7% with tamoxifen+ovarian suppression, and 80,5% with exemestane+ovarian suppression; an overall survival advantage was also demonstrated in this high-risk subgroup. The ATLAS study (Lancet 2013) showed that continuing tamoxifen for 10 rather than 5 years reduced recurrence risk by 25% and the risk of death from breast cancer by 29%, particularly after year 10 — the benefit mainly emerged after the first 5 years of treatment.
Adding a CDK4/6 inhibitor to endocrine therapy has become standard in high-risk hormone receptor-positive, HER2-negative early-stage patients — but eligibility criteria differ between the two approved drugs. Abemaciclib (monarchE study) is used for 2 years in patients with ≥4 positive lymph nodes or 1-3 positive nodes + (tumor ≥5cm or grade 3); at 5-year follow-up it provided an absolute 7,6% improvement in disease-free survival (HR 0,68), but the 2024 interim overall survival analysis was not yet statistically significant (HR 0,90). FDA approval was on 12 October 2021 (initially only for Ki-67≥20%); on 3 March 2023 it was expanded by removing this requirement. Ribociclib (NATALEE study) covers a broader population — including high-risk node-negative patients (with large tumors or high grade/genomic risk); it is used for 3 years. 3-year disease-free survival was 90,4% versus 87,1% (HR 0,75, absolute benefit 3,3%); FDA approval was on 17 September 2024. Practical difference: NATALEE's eligibility criteria are broader than monarchE's and include high-risk node-negative patients.
The TAILORx study (NEJM 2018) showed that endocrine therapy alone was sufficient in patients with a Recurrence Score (RS) of 0-10 and that adding chemotherapy provided no additional benefit; no chemotherapy benefit was demonstrated overall in the RS 11-25 range, but a limited benefit was observed in the subgroup aged ≤50 with RS 16-25. Chemotherapy is recommended for RS 26 and above. The RxPONDER study (NEJM 2021), in patients with 1-3 positive nodes and RS 0-25, showed that in postmenopausal women adding chemotherapy provided no additional benefit (chemotherapy can be omitted), whereas in premenopausal women it provided a significant benefit — an important finding showing that menopausal status can change the treatment decision within the same RS range.
HER2-Positive
Adjuvant trastuzumab (for 1 year, with chemotherapy) has long been standard in HER2-positive early-stage disease. The APHINITY study (NEJM 2017, 8-year update) showed that the benefit of adding pertuzumab to trastuzumab (dual HER2 blockade) was concentrated mainly in node-positive patients: disease-free survival in this subgroup was 86,1% versus 81,2% (absolute benefit 4,9%, HR 0,72); no significant benefit was shown in node-negative patients (92,3% versus 93,3%). Adding pertuzumab is therefore primarily intended for node-positive patients. FDA approval (adjuvant pertuzumab): December 2017.
In HER2-positive patients, preoperative (neoadjuvant) taxane+trastuzumab+pertuzumab (THP) or TCHP (with added carboplatin) regimens are generally preferred; this approach both shrinks the tumor to enable breast-conserving surgery and directly shows treatment response (whether a pathological complete response occurs). The KATHERINE study (NEJM 2019, 7-year long-term follow-up) showed that, in patients with residual invasive disease detected at surgery after neoadjuvant treatment, giving adjuvant treatment with T-DM1 (trastuzumab emtansine) instead of trastuzumab significantly improved outcomes: 7-year disease-free survival was 80,8% versus 67,1% (~46% reduction in invasive recurrence or death risk); 7-year overall survival was 89,1% versus 84,4%. FDA approval: 3 May 2019. This finding is one of the clearest examples of the principle of "a different adjuvant strategy for patients without a complete response to neoadjuvant treatment."
For small (≤3cm), node-negative HER2-positive tumors, the less intensive weekly paclitaxel+trastuzumab regimen was evaluated. According to the final 10-year analysis of the APT study (Lancet Oncology 2023), 10-year disease-free survival with this de-escalated regimen was reported as 91,3%, and overall survival as 94,3% — showing that less intensive treatment can also provide excellent results in selected small tumors.
Triple-Negative (TNBC)
In triple-negative patients with tumors >1-2cm and lymph node involvement or tumors >2cm (regardless of lymph node status), adding pembrolizumab to neoadjuvant chemotherapy (paclitaxel+carboplatin followed by anthracycline+cyclophosphamide) and continuing pembrolizumab after surgery has become standard. In KEYNOTE-522, the pathological complete response rate was 63,0% versus 55,6% (placebo); 7-year event-free survival was 78,3% versus 69,8% (HR 0,68). Newly matured overall survival data presented at ASCO in 2026 showed 7-year overall survival of 85,1% versus 77,2% (HR 0,64) — an important current finding confirming that the pCR/EFS benefit translates into a true survival advantage. FDA approval: 26 July 2021.
In HER2-negative patients with residual invasive disease after neoadjuvant chemotherapy, adding adjuvant capecitabine (CREATE-X study, NEJM 2017) increased 5-year disease-free survival from 67,6% to 74,1% and overall survival from 83,6% to 89,2%; the benefit was even more pronounced in the triple-negative subgroup. In high-risk HER2-negative patients with a germline BRCA1/2 mutation, adding treatment for 1 year after (neo)adjuvant chemotherapy with olaparib (OlympiA study, NEJM 2021/2022) provided a significant improvement in disease-free survival with HR 0,58 and a 3-year overall survival benefit of 92,0% versus 88,3%. FDA approval: 11 March 2022.
Treatment of Metastatic (Stage IV) Breast Cancer
Although metastatic breast cancer cannot currently be treated curatively, modern treatments have greatly improved survival and quality of life — in hormone receptor-positive and HER2-positive patients, median survival can exceed 3 years in many series. Treatment is planned separately by molecular subtype and generally proceeds through first, second, and third lines and beyond : when disease becomes resistant to a regimen, the next treatment targeting a different mechanism is introduced.
Hormone Receptor-Positive, HER2-Negative Metastatic Disease
First-Line Treatment
Standard first-line treatment combines a CDK4/6 inhibitor with an aromatase inhibitor. All three drugs are approved, but their results have been reported at different levels of maturity: PALOMA-2 (palbociclib+letrozole): PFS 24,8 months vs 14,5 months (HR 0,58); final OS 53,9 vs 51,2 months, not statistically significant (p=0,34). MONALEESA-2 (ribociclib+letrozole): PFS 25,3 vs 16,0 months (HR 0,56); final OS 63,9 vs 51,4 months (HR 0,76) — statistically significant and the longest reported median overall survival among these three studies. MONARCH 3 (abemaciclib+nonsteroidal AI): PFS 28,2 vs 14,8 months (HR 0,54); OS 66,8 vs 53,7 months, not statistically significant (p=0,066). Important clinical nuance: only ribociclib has demonstrated a statistically significant overall survival benefit in the first line; numerically longer OS was observed with the other two drugs, but the significance threshold was not reached — this distinction matters when informing patients.
Second-Line Treatment
If a CDK4/6 inhibitor was not used in the first line (or, rarely, when switching to a different CDK4/6i), a CDK4/6 inhibitor+fulvestrant combination is considered in the second line: PALOMA-3 (palbociclib+fulvestrant) PFS 9,5 vs 4,6 months; MONALEESA-3 (ribociclib+fulvestrant) PFS 20,5 vs 12,8 months, OS 67,6 vs 51,8 months (HR 0,67); MONARCH 2 (abemaciclib+fulvestrant) PFS 16,4 vs 9,3 months, OS 46,7 vs 37,3 months. When resistance to first-line CDK4/6i develops, treatment is guided by the tumor's molecular profile: PIK3CA mutation : if present, alpelisib+fulvestrant (SOLAR-1, PFS 11,0 vs 5,7 months, HR 0,65; FDA approval 24 May 2019); AKT1/PIK3CA/PTEN alteration : if present, capivasertib+fulvestrant (CAPItello-291, PFS 7,3 vs 3,1 months, HR 0,50; FDA approval 16 November 2023); ESR1 mutation : if present, an oral SERD (selective estrogen receptor degrader), elacestrant (EMERALD, PFS 3,8 vs 1,9 months in the ESR1-mutant subgroup, HR 0,55; FDA approval 27 January 2023), or imlunestrant (EMBER-3, PFS 5,5 vs 3,8 months, HR 0,62; FDA approval 25 September 2025, the second approved oral SERD) is considered. These three drugs are concrete examples of "treating according to the mutation present" and require an updated mutation assessment through repeat biopsy or liquid biopsy (ctDNA) before treatment.
Third-Line Treatment and Beyond
When endocrine treatment options are exhausted, antibody-drug conjugates (ADCs) come into use. Sacituzumab govitecan (targeting TROP-2), in the TROPiCS-02 study, produced PFS of 5,5 vs 4,0 months and OS of 14,4 vs 11,2 months (HR 0,79) in hormone receptor-positive patients and received approval for this indication on 3 February 2023. Trastuzumab deruxtecan (T-DXd) is effective in HER2-low (DESTINY-Breast04, PFS 10,1 vs 5,4 months, OS 23,9 vs 17,5 months; FDA approval 5 August 2022 — this approval made the "HER2-low" category treatable for the first time) and HER2-ultralow (DESTINY-Breast06, PFS 13,2 vs 8,1 months in patients without chemotherapy after hormonal treatment, response rate 62,6% vs 34,4%; approval expansion approximately January 2025) patients. These two drugs demonstrate why the HER2-low/ultralow category defined above matters in clinical practice.
HER2-Positive Metastatic Disease
First-Line Treatment
Standard first-line treatment combines a taxane (docetaxel/paclitaxel) with trastuzumab+pertuzumab (THP). The final analysis of the CLEOPATRA study (Swain, NEJM 2020) showed median overall survival of 57,1 months versus 40,8 months (HR 0,69) — an absolute difference of 16,3 months — one of the largest absolute overall survival differences reported to date in any solid tumor, making THP the long-established, undisputed first-line standard in metastatic HER2-positive disease.
Second-Line Treatment
In patients progressing after THP, the previous second-line standard, T-DM1, has now been replaced by trastuzumab deruxtecan . The DESTINY-Breast03 study demonstrated a striking advantage of T-DXd over T-DM1: median PFS was not reached in the T-DXd arm, whereas it was only 6,8 months in the T-DM1 arm (HR 0,28); response rate was 82,7% versus 36,1%. FDA approval (conversion to regular approval): 4 May 2022. These results made T-DXd the new second-line standard.
Third-Line Treatment and Beyond
The HER2CLIMB study showed that tucatinib+trastuzumab+capecitabine benefited the overall population (PFS 7,8 vs 5,6 months, OS 21,9 vs 17,4 months), but more importantly, that it was also effective in patients with brain metastases : in the brain metastasis subgroup, central nervous system PFS was 9,9 vs 4,2 months (HR 0,32), and overall survival was 18,1 vs 12,0 months (HR 0,58); the benefit persisted even in patients with active (not yet treated/progressing) brain metastases. FDA approval: 17 April 2020 — the first approval specifically based on central nervous system activity in HER2-positive metastatic disease, making it an important option for patients with brain metastases. Other later-line options include margetuximab (SOPHIA study, PFS 5,8 vs 4,9 months) and neratinib (combined with capecitabine, NALA study).
Triple-Negative Metastatic Disease
First-Line Treatment
In PD-L1-positive (combined positive score, CPS≥10, by the 22C3 test) metastatic triple-negative patients, adding pembrolizumab to first-line chemotherapy is standard. In KEYNOTE-355, PFS was 9,7 vs 5,6 months (HR 0,65); final overall survival was 23,0 vs 16,1 months (HR 0,73). FDA approval: 13 November 2020. No benefit from adding immunotherapy was demonstrated in PD-L1-negative patients; therefore, PD-L1 testing determines treatment selection.
Second-Line Treatment and Beyond
In advanced triple-negative disease (after at least 2 previous chemotherapy lines), sacituzumab govitecan showed a significant benefit in ASCENT, with PFS 5,6 vs 1,7 months (HR 0,41) and OS 12,1 vs 6,7 months (HR 0,48) (regular approval 7 April 2021). PARP inhibitors may be considered in patients with germline BRCA1/2 mutations: olaparib (OlympiAD, PFS 7,0 vs 4,2 months, HR 0,58; however, no significant overall survival difference was shown, 19,3 vs 19,6 months) and talazoparib (EMBRACA, PFS 8,6 vs 5,6 months, HR 0,54; no significant overall survival difference was shown here either). These two PARP studies are an important example of an unproven overall survival benefit despite strong PFS/response-rate benefits, and this distinction must be made explicit when counseling patients.
Bone-Directed Treatment
In patients of all subtypes with bone metastases, to reduce skeletal-related events such as pathological fractures and spinal cord compression, treatment uses zoledronic acid or denosumab . A head-to-head study (Stopeck et al., JCO 2010) showed that denosumab was superior to zoledronic acid in delaying the first skeletal event and carried no renal toxicity, but its risks of hypocalcemia and osteonecrosis of the jaw could be slightly higher.
Special Populations
In women carrying BRCA1/2 mutations, preventive bilateral mastectomy and/or bilateral salpingo-oophorectomy (removal of the ovaries and fallopian tubes) may be considered to reduce contralateral breast cancer risk; bilateral mastectomy reduces breast cancer risk by approximately 90-95%. Early-stage BRCA-associated breast cancer follows general treatment principles; adjuvant olaparib based on OlympiA for high-risk HER2-negative disease and olaparib/talazoparib based on OlympiAD/EMBRACA for metastatic disease are important additional options (discussed in detail above).
Pregnancy after breast cancer has not been shown to adversely affect survival; however, in hormone receptor-positive disease, pregnancy planning must be timed with the physician because of prolonged endocrine treatment. For breast cancer during pregnancy, surgery is considered safe in every trimester, while chemotherapy may be administered in the second and third trimesters; endocrine and anti-HER2 treatments are deferred until after delivery, and radiotherapy is generally also postponed until after delivery.
Some chemotherapy regimens can cause early/temporary menopause in premenopausal women. Fertility preservation options, such as embryo or oocyte freezing, should be discussed before gonadotoxic treatment begins. Absence of menstruation during treatment does not mean that a patient is postmenopausal; contraception must therefore continue.
Treatment decisions consider biological/functional age more than chronological age; healthy, fit older patients can receive treatments similar to younger patients. Standard regimens may be individualized in frail patients with attention to the treatment benefit-risk balance; omitting radiotherapy after breast-conserving surgery may be an option for selected older patients with small hormone receptor-positive tumors who will receive endocrine therapy.
Breast cancer in men is rare, and the vast majority of cases are hormone receptor-positive; treatment principles resemble those for female breast cancer, and standard adjuvant/metastatic endocrine therapy is tamoxifen (aromatase inhibitors may be less effective when used alone in men because there is no ovarian suppression, so they are generally considered with a GnRH analogue). A pathology review is recommended for male patients diagnosed as triple-negative or HER2-positive because these profiles are less expected in men.
Treatment-Related Side Effects and Their Management
Surgery and Lymphedema
Patients with axillary lymph nodes removed may develop lymphedema (swelling) in the arm and breast area; this rate is significantly higher after complete axillary dissection than after sentinel lymph node biopsy. Early postoperative assessment by a physical therapy and rehabilitation team, exercise programs, and lymphedema massage when needed are important for reducing risk; maintaining a healthy weight and regularly using the operated arm are also protective.
Radiotherapy
The most common side effects are fatigue, skin irritation, and pain/swelling in the treated area. Breast radiotherapy may expose the heart and lungs to some radiation; modern techniques (breath-hold techniques, IMRT) have greatly reduced this risk.
Chemotherapy
The side-effect profile of chemotherapy varies with the drug used; the most commonly affected tissues are bone marrow (risk of neutropenia, anemia, thrombocytopenia), hair follicles, the digestive system, and oral mucosa. Nausea/vomiting can now largely be prevented with effective drugs; neutropenic fever requires urgent assessment.
Chemotherapy-related hair loss is one of the most distressing side effects for patients. Cooling the scalp during chemotherapy infusion can significantly reduce hair loss by reducing blood flow to hair follicles and thus the drug's effect on them; the FDA approved cooling devices for this purpose in 2015. Success varies with drug type, dose, and number of administrations; the method is not used in hematological cancers.
Endocrine Therapy and CDK4/6 Inhibitors
Side effects of endocrine therapy are largely due to reduced estrogen levels: hot flashes, increased sweating, and vaginal dryness. Aromatase inhibitors can cause joint pain/stiffness and loss of bone density (osteoporosis); regular bone mineral density monitoring and adequate calcium/vitamin D intake are therefore recommended. CDK4/6 inhibitors are associated with neutropenia, fatigue, and diarrhea (particularly abemaciclib); regular blood count monitoring is required.
FDA Approval Timeline: The Evolution of Systemic Breast Cancer Treatment
Trastuzumab The First HER2-Targeted Therapy
The first HER2-targeted therapy approved for breast cancer; a milestone in HER2-positive breast cancer treatment.
Lapatinib
The first oral HER2 tyrosine kinase inhibitor was approved.
Pertuzumab
Based on the CLEOPATRA study, the first drug targeting HER2 dimerization was approved; it subsequently became a standard component of the THP regimen.
T-DM1 (Trastuzumab Emtansine) The First Antibody-Drug Conjugate
Based on the EMILIA study, the first antibody-drug conjugate (ADC) approved for breast cancer.
Palbociclib The First CDK4/6 Inhibitor
Based on the PALOMA-1 study, the first CDK4/6 inhibitor approved for any cancer type.
Ribociclib
The second CDK4/6 inhibitor, approved on the basis of the MONALEESA-2 study.
Abemaciclib
The third CDK4/6 inhibitor; the only CDK4/6 inhibitor also approved as monotherapy.
Olaparib The First PARP Inhibitor
Based on the OlympiAD study, the first PARP inhibitor approved for breast cancer (germline BRCA mutation).
Talazoparib
The second PARP inhibitor, approved on the basis of the EMBRACA study.
Alpelisib The First PI3K Inhibitor
Based on the SOLAR-1 study, the first PI3K inhibitor approved for breast cancer (PIK3CA mutation).
Tucatinib The First Brain-Metastasis-Specific Approval
Based on the HER2CLIMB study, the first approval in HER2-positive breast cancer specifically based on central nervous system (brain metastasis) activity.
Atezolizumab + Nab-Paclitaxel The First Immunotherapy to Be Withdrawn
Based on the IMpassion130 study, it was the first cancer immunotherapy approved for breast cancer; after the failure of the confirmatory IMpassion131 study, the manufacturer voluntarily withdrew it on 27 August 2021 — an important example of the risks of the accelerated approval system.
Sacituzumab Govitecan The First Trop-2 ADC
Based on the ASCENT study, the first Trop-2-targeted antibody-drug conjugate approved for any cancer.
Pembrolizumab + Chemotherapy
Based on the KEYNOTE-355 study, a durable immunotherapy approval was achieved for PD-L1-positive triple-negative metastatic disease.
Trastuzumab Deruxtecan (HER2-Low) The Emergence of the "HER2-Low" Category
Based on the DESTINY-Breast04 study, this field-redefining approval demonstrated that tumors below the conventional HER2-positivity threshold could also benefit from targeted therapy.
Trastuzumab Deruxtecan (2nd Line)
Based on the DESTINY-Breast03 study, it demonstrated a striking advantage over T-DM1 and became the second-line standard.
Elacestrant The First Oral SERD
Based on the EMERALD study, the first oral selective estrogen receptor degrader (SERD), used in patients carrying ESR1 mutations.
Capivasertib The First AKT Inhibitor
Based on the CAPItello-291 study, the first AKT inhibitor approved for breast cancer (AKT1/PIK3CA/PTEN alteration).
Trastuzumab Deruxtecan (HER2-Ultralow) "HER2-Ultralow" Approval
Based on the DESTINY-Breast06 study, it further expanded treatment eligibility to tumors with the lowest detectable levels of HER2 expression.
Ribociclib (Early Stage/Adjuvant)
Based on the NATALEE study, it received a broad early-stage adjuvant approval also covering high-risk node-negative patients.
Imlunestrant
The second oral SERD, approved on the basis of the EMBER-3 study.
Camizestrant, based on the SERENA-6 study testing early treatment switching (before radiographic progression, based only on a ctDNA/ESR1 mutation detected in blood), as of the date this guide was prepared (August 2026) had not yet received FDA approval in the United States — the FDA advisory committee (ODAC) did not deliver a favorable opinion in April 2026, and the decision date was extended; in contrast, the European Medicines Agency (EMA) granted approval on 22 May 2026. This is a current example of differing regulatory decisions, and the situation may change rapidly.
Screening, Licensing, and Reimbursement Status in Türkiye
In Turkey, through Cancer Early Diagnosis, Screening and Education Centers (KETEM) affiliated with the Ministry of Health, free mammography every 2 years for women aged 40-69 is offered as a screening service. This program aligns with the United States Preventive Services Task Force (USPSTF) 2024 update in terms of its starting age (40), but its upper age limit (69) ends earlier than the USPSTF's age of 74; compared with the traditional starting age of 50 in many European countries, Turkey's program starts earlier.
According to our sources, trastuzumab, pertuzumab (for HER2-positive disease) and the agents used in metastatic disease, palbociclib and ribociclib (CDK4/6 inhibitors), are authorized in Turkey and covered by SGK; denosumab is also covered for bone metastases without requiring additional approval. Pembrolizumab, with the SUT (Healthcare Implementation Communiqué) update dated 10 July 2025, was included in SGK coverage for triple-negative breast cancer — according to our sources, this coverage appears to include at least neoadjuvant use (with criteria similar to KEYNOTE-522, tumor ≥2cm and/or lymph node positivity); whether the metastatic (KEYNOTE-355) indication is also included in this coverage is unclear and has not been verified.
According to our sources, the following more recently approved drugs have TİTCK authorization in Turkey, but as of the date this article was prepared, SGK does not cover them and patients generally have to resort to legal proceedings (interim injunction/lawsuit) to access them: trastuzumab deruxtecan (Enhertu), sacituzumab govitecan (Trodelvy), alpelisib (Pimreva) and elacestrant (Orserdu, authorized in November 2025). T-DM1 (Kadcyla) is likewise described by one source as being outside reimbursement coverage. Capivasertib (Truqap) and talazoparib (Talzenna)have current authorization/reimbursement statuses in Turkey that could not be clearly verified in this research. Whether SGK covers CDK4/6 inhibitor use in early-stage disease (for the adjuvant monarchE/NATALEE indications) could also not be confirmed as of the date this article was prepared — this should not be confused with metastatic use. The exact conditions for SGK coverage of BRCA1/2 germline genetic testing were also not verified in this research; direct confirmation with genetic counseling centers or SGK is recommended for current information.
Frequently Asked Questions
- Does breast cancer always present as a lump?
- No. Some types, such as inflammatory breast cancer, may present with skin redness, increased warmth and an orange-peel appearance without a distinct lump. Any persistent breast change must be evaluated.
- Am I not at risk if there is no breast cancer in my family?
- No, the vast majority of breast cancer cases occur in women without a family history. Family history and genetic mutations are important factors that increase risk, but they are not the sole determinants.
- Why does the "prognostic stage" in my pathology report differ from the "anatomic stage" I previously knew?
- The AJCC 8th edition staging system can shift the anatomic stage up or down by also considering the tumor grade and hormone receptor/HER2 status. This is not an error, but an expected result of incorporating tumor biology into staging.
- Does every hormone receptor-positive patient need chemotherapy?
- No. Genomic tests such as Oncotype DX have shown that chemotherapy offers no additional benefit for many patients with a low recurrence score and that endocrine therapy alone may be sufficient. The decision is individualized according to the test result, lymph node status and menopausal status.
- Does a diagnosis of metastatic breast cancer mean there are no treatment options left?
- No. Although metastatic breast cancer cannot currently be treated curatively, many effective systemic treatment options specific to each subtype are available, and treatments can prolong survival by years; treatment continues step by step, moving to the next option as the disease progresses.
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