What Is Carcinoma? The Most Common Cell Type in Cancer
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Cancer is not a single disease; it is a collective name for hundreds of diseases that behave very differently depending on the cell from which they arise. Carcinoma is the largest member of this family: it is the name for cancers arising from the epithelial cells that cover the body's internal and external surfaces, and it accounts for 80-90% of all cancers. This article explains what the word "carcinoma" means, how it differs from sarcoma and lymphoma, the crucial difference between in situ and invasive disease, and how a pathologist identifies a tumor as a "carcinoma."
Article Summary
- Carcinoma = epithelial-origin cancer. Sarcoma arises from connective tissue, lymphoma and leukemia from blood cells, and melanoma from pigment cells — melanoma is not a carcinoma.
- Carcinomas account for 80-90% of all cancers. Because most skin cancers are never included in the statistics, the true proportion is even higher.
- The article's most important concept: the basement membrane. In situ carcinoma has not crossed this membrane and cannot spread; invasive carcinoma has crossed it.
- Grade and stage are not the same thing. Grade describes how abnormal the cells look; stage describes how far the disease has spread.
- Of the 10 most common cancers in Turkey, almost all are carcinomas.
Where Do Cancers Originate? Four Main Groups
Epithelium is the cell layer covering all the body's surfaces: the skin, airways of the lungs, inner surface of the bowel, breast and prostate ducts, kidney tubules and inner bladder lining. Its functions are protection, secretion, absorption and filtration. Cancers arising from epithelium are called carcinomas.
Distribution of Cancers by Cell of Origin
Derived from US 2026 estimates; nonmelanoma skin cancers are not included in these statistics
Carcinoma (epithelium)
~83%
Lymphoma, leukemia, myeloma (blood)
9.1%
Melanoma (pigment cell)
5.3%
Brain and nervous system
1.2%
Sarcoma (connective tissue, bone, muscle)
0.9%
Germ cell tumors (testis)
0.5%
The official wording of the US National Cancer Institute is: "Carcinomas, which are malignant diseases of epithelial tissue, account for 80 to 90% of all cancer cases." The distribution above is an approximation calculated from 2026 estimates and is consistent with this range. Important note: cancer registries do not count basal and squamous cell skin cancers at all. In the USA alone, approximately 5.4 million basal and squamous cell skin cancers are diagnosed annually, and all are carcinomas. If counted, the carcinoma proportion would exceed 95%. Thus, 80-90% is a cautious figure.
What Does the Ending Mean? "-oma," "-carcinoma," "-sarcoma," "-blastoma"
| Suffix | Meaning | Examples |
|---|---|---|
| -om / -oma (on its own) | Usually a benign tumor, named according to its tissue of origin | lipoma (fat), fibroma (connective tissue), adenoma (gland), myoma (smooth muscle), osteoma (bone) |
| -carcinoma | Malignant, epithelial origin | adenocarcinoma, squamous cell carcinoma, basal cell carcinoma, renal cell carcinoma |
| -sarcoma | Malignant, connective tissue/mesenchymal origin | osteosarcoma (bone), liposarcoma (fat), leiomyosarcoma (smooth muscle), angiosarcoma (blood vessel) |
| -blastoma | Malignant, embryonic precursor cell origin; predominantly in childhood | neuroblastoma, nephroblastoma (Wilms tumor), retinoblastoma, hepatoblastoma, medulloblastoma |
Dangerous exceptions: names ending in "-oma" that are not benign.
- Melanoma — arises from melanocytes, pigment cells of neural crest origin. These are not epithelial cells; therefore, melanoma is not a carcinoma. Although it develops in the skin, it is not biologically related to basal and squamous cell carcinomas. Grouping all three under "skin cancer" obscures a fundamental difference.
- Lymphoma — a malignant disease arising from lymphocytes.
- Myeloma — from plasma cells.
- Seminoma — from germ cells.
- Glioma / glioblastoma — from glial cells in the brain.
The Article's Most Important Concept: The Basement Membrane
Beneath every epithelial layer is a thin structural membrane separating it from the underlying connective tissue: the basement membrane. Blood vessels and lymphatic channels are located beneath this membrane. This simple anatomical fact creates the most important boundary in cancer biology.
In situ carcinoma
Under the microscope, the cells look like cancer cells, but they have not crossed the basement membrane. They cannot physically reach blood vessels and lymphatic channels. Therefore, they cannot metastasize and complete removal usually provides a cure. It is classified as Stage 0.
Invasive carcinoma
The cells have penetrated the basement membrane and entered the underlying tissue. Only from this point do vascular and lymphatic invasion, spread to lymph nodes and distant metastasis become possible.
Why Is This So Important?
Because this single anatomical event separates a lesion with a very high chance of cure from a potentially life-threatening disease. Seeing "in situ" in a pathology report means that the disease belongs to an entirely different category.
Common examples of in situ carcinoma include: DCIS (in breast ducts), cervical carcinoma in situ / HSIL (associated with HPV), urothelial carcinoma in situ of the bladder (an exception that is high-grade and carries a high progression risk), and Bowen disease (squamous cell carcinoma in situ of the skin).
Grade Must Not Be Confused With Stage
| Grade | Stage | |
|---|---|---|
| What does it measure? | Under the microscope, how abnormal the cells look | The disease's extent of spread |
| Who determines it? | The pathologist, using a microscope | Imaging, surgical findings and pathology together |
| Categories | G1 well differentiated (low grade) → G2 moderately differentiated → G3 poorly differentiated (high grade) → G4 undifferentiated | Stage 0 (in situ) → Stage I-III (progressively more advanced) → Stage IV (distant metastasis) |
| Meaning | The more the cells resemble normal cells, the more slowly the tumor grows and spreads; the more abnormal they look, the more aggressive it is | T: size and extent of the primary tumor · N: number of involved lymph nodes · M: presence of distant metastasis |
In Turkish, these two concepts are often used interchangeably, causing serious misunderstandings for patients. "Stage 1 but grade 3" is not a contradiction: the disease is at an early stage, but the cells look aggressive. "Stage 4 but grade 1" is also possible.
How Does a Pathologist Identify a Tumor as "Carcinoma"?
Under the microscope, a poorly differentiated tumor may look like nothing more than a "mass of malignant cells"; its tissue of origin cannot be recognized by appearance. This is where immunohistochemistry (IHC) comes in: antibodies that stain particular proteins are applied to the tissue.
| Origin | Staining markers |
|---|---|
| Carcinoma (epithelium) | Pan-cytokeratin (AE1/AE3), CAM5.2, EMA |
| Lymphoma | CD45 / LCA; then CD20 (B cell), CD3 (T cell) |
| Melanoma | S100, SOX10, HMB-45, Melan-A — cytokeratin negative |
| Sarcoma | Vimentin; then tissue-specific markers such as desmin (muscle), CD31/ERG (blood vessel) |
Cytokeratin positivity is the most decisive finding in this panel: it indicates epithelial differentiation and therefore carcinoma. The second step is to find which organ the carcinoma came from. The most commonly used approach is the CK7/CK20 four-quadrant algorithm:
| CK20 negative | CK20 positive | |
|---|---|---|
| CK7 positive | Lung, breast, thyroid, ovary (serous/endometrioid), endometrium, cervix, pancreas (most), bile ducts, esophageal adenocarcinoma, stomach (most), salivary gland, mesothelioma | Urothelial carcinoma, pancreas (some), stomach (some), small bowel, mucinous ovarian, extrahepatic bile duct |
| CK7 negative | Prostate, renal cell carcinoma, hepatocellular carcinoma, adrenocortical carcinoma, germ cell tumors, squamous cell carcinoma | Colorectal carcinoma, Merkel cell carcinoma |
The third step uses organ-specific transcription factors: TTF-1 (lung, thyroid), CDX2 and SATB2 (bowel), GATA3 (breast, urothelium), PAX8 (kidney, thyroid, ovary, endometrium), NKX3.1 and PSA (prostate), p40 and p63 (squamous differentiation), ER/PR (breast), WT1 and calretinin (serous ovarian, mesothelioma).
Realistic expectations. Immunohistochemistry narrows the possibilities but usually does not provide certainty. In ESMO's wording, staining patterns can identify the origin of cancers of unknown primary in fewer than 30% of cases.
Main Types of Carcinoma
Skin Carcinomas: Basal and Squamous Cell
Basal cell carcinoma (BCC) is the most common cancer type, accounting for approximately 80% of skin cancers. It arises from the lowest layer of the epidermis, occurs in sun-exposed areas—especially the face—and very rarely metastasizes. Signs include a nonhealing open sore, a pearly shiny bump, or a patch that crusts or bleeds.
| Basal cell carcinoma treatment | Indication | 5-year recurrence |
|---|---|---|
| Mohs micrographic surgery | All high-risk lesions: face, hands, feet, genital area; recurrent lesions; aggressive subtypes | 1.0% |
| Standard surgical excision | Low-risk trunk and limb lesions (4 mm margin) | 10.1% |
| Curettage and electrodesiccation | Small, superficial lesions in non-hair-bearing areas | 7.7% |
| Cryotherapy | Selected superficial lesions | 7.5% |
| Radiotherapy | Patients unsuitable for surgery; additional treatment for perineural invasion | 8.7% |
| Topical imiquimod / 5-fluorouracil | Superficial BCC only | Clearance 73-82%; high recurrence rate |
| Photodynamic therapy | Superficial and nodular BCC | Cure: 50% for superficial, 83% for nodular |
Drug treatment for advanced basal cell carcinoma. For locally advanced or metastatic BCC unsuitable for surgery and radiotherapy, there are two lines of treatment:
- Hedgehog pathway inhibitors: vismodegib (FDA approval 30 January 2012)—response rate in locally advanced disease: 60.3%, and 48.5% in metastatic disease; median response duration 26.2 months. Sonidegib (24 July 2015)—response rate in locally advanced disease: 56%.
- Immunotherapy: cemiplimab (9 February 2021), after a Hedgehog inhibitor or in patients unsuitable for one—response rate in locally advanced disease: 29%, and 21% in metastatic disease.
Squamous cell carcinoma (SCC) is the second most common skin cancer, arising from flat, fish-scale-like cells. Unlike BCC, it can metastasize. Risk factors include fair skin, cumulative sun exposure, age over 50, immunosuppression (especially organ transplantation) and HPV.
Immunotherapy is also standard in advanced cutaneous SCC: cemiplimab (28 September 2018), response rate 47%; pembrolizumab (24 June 2020), response rate 34%, and 50% in locally advanced disease (6 July 2021). New: On 8 October 2025, cemiplimab was also approved after surgery and radiotherapy for cutaneous SCC at high risk of recurrence, as additional (adjuvant) treatment —in the C-POST study, disease-free survival had an HR of 0.32.
Note: squamous cell carcinoma first brings the skin to mind, but it also occurs in the lung, esophagus, head and neck, and cervix, where its behavior is entirely different.
Note: squamous cell carcinoma first brings the skin to mind, but it also occurs in the lung, esophagus, head and neck, and cervix, where its behavior is entirely different.
Adenocarcinoma: The Most Common Form of Carcinoma
Adenocarcinoma is carcinoma arising from secretory glandular epithelium. Many of the body's deadliest cancers belong to this group.
| Organ | Proportion that is adenocarcinoma |
|---|---|
| Prostate | Of primary prostate cancers, more than 95% |
| Stomach | Of gastric malignancies, 90-95% |
| Pancreas | Ductal cell carcinoma 90% |
| Colorectal | The vast majority |
| Lung | Approximately 40-50% and rising (squamous cell 20-30% and declining) |
| Esophagus | Has overtaken squamous cell carcinoma in Western countries; squamous cell carcinoma still leads worldwide |
Breast: DCIS and Invasive Carcinoma
Ductal carcinoma in situ (DCIS) is carcinoma confined to the breast ducts that has not crossed the basement membrane. It accounts for approximately 16% of diagnosed breast cancers (up to 20% in screening mammography literature). It usually causes no symptoms and is detected on routine mammography.
How Much Does DCIS Progress? The honest answer is that we do not know for certain. The best data come from retrospective examination of cases initially thought to be benign and left untreated; in these series, 46-53% subsequently developed invasive cancer. By contrast, autopsy studies find unrecognized DCIS in up to 14.7% of women, and most of these lesions never progress. DCIS is now considered a "nonobligate precursor lesion".
New development: for low-risk DCIS, active monitoring instead of surgery is being investigated. In the COMET study (n=995, JAMA 2024), the two-year invasive cancer rate was 5.9% with guideline-concordant treatment and 4.2% with active monitoring; active monitoring was not inferior. Initial results of LORD reported in 2026 point in a similar direction. This is not yet standard, but it suggests that not every case of DCIS may require surgery.
New development: for low-risk DCIS, active monitoring instead of surgery is being investigated. In the COMET study (n=995, JAMA 2024), the two-year invasive cancer rate was 5.9% with guideline-concordant treatment and 4.2% with active monitoring; active monitoring was not inferior. Initial results of LORD reported in 2026 point in a similar direction. This is not yet standard, but it suggests that not every case of DCIS may require surgery.
A terminology correction: in DCIS, hormone therapy is not treatment for DCIS itself — it is a method of reducing the risk of subsequent breast cancer events. In NSABP B-24, tamoxifen reduced 5-year breast cancer events from 13.4% to 8.2%. This distinction matters in terms of what is promised to the patient.
Invasive carcinoma has crossed the basement membrane. Its most common type, previously called "invasive ductal carcinoma," accounts for 75-80% of invasive breast cancers. The World Health Organization now prefers the term "invasive carcinoma of no special type (NST)" for this tumor, because "ductal" wrongly suggests that it arises from a duct cell. In fact, NST means a tumor that does not have the defining characteristics of a special subtype, such as lobular, mucinous or tubular.
Renal Cell Carcinoma
Renal cell carcinoma (RCC) accounts for more than 90% of adult kidney malignancies. It arises from the epithelium of the tubules that filter blood in the kidneys. Subtypes include: clear cell 70-80%, papillary 10-15% and chromophobe approximately 5%. It is silent early on; with progression, flank pain, blood in urine, weight loss and anemia may occur.
Important correction: renal cell carcinoma is resistant to chemotherapy and radiotherapy. In a review of 4,093 patients, the overall response rate to cytotoxic chemotherapy in advanced RCC was only 6%. Radiotherapy is not a systemic treatment for metastatic disease either; it is used for palliation, such as bone or brain metastases, or selected oligometastatic sites.
Today's standard in metastatic RCC is immunotherapy-based combinations:
Today's standard in metastatic RCC is immunotherapy-based combinations:
- Nivolumab + ipilimumab (CheckMate 214): at 8 years of follow-up, median survival 53 months versus 38 months (HR 0.72); complete response 12% versus 3%. Note: the registered indication is for intermediate- and poor-risk patients; superiority was not shown in the favorable-risk subgroup.
- Pembrolizumab + axitinib (KEYNOTE-426): median survival 47.2 versus 40.8 months; response rate 60.6% versus 39.6%.
- Nivolumab + cabozantinib (CheckMate 9ER): median survival 46.5 versus 35.5 months; median PFS 16.4 versus 8.3 months.
- Lenvatinib + pembrolizumab (CLEAR): median survival 53.7 months.
Urothelial (Transitional Cell) Carcinoma
It arises from the urothelium lining the urinary tract: the renal collecting system, ureter, bladder and urethra. Two separate facts are often confused; both need to be stated correctly:
| Question | Answer |
|---|---|
| What proportion of bladder cancers are urothelial carcinomas? | More than 90%. Squamous cell carcinoma 2-7%, adenocarcinoma approximately 2%. |
| Where do urothelial carcinomas occur? | 90-95% are in the bladder; the upper urinary tract (renal pelvis and ureter) accounts for only 5-10%. Renal pelvis tumors are approximately twice as common as ureteral tumors. |
Related topic: Symptoms and treatment of stage 4 bladder cancer
Neuroendocrine Carcinoma and Small Cell Carcinoma
Neuroendocrine cells are epithelial cells with both neural and hormone-secreting properties. Under the 2022 World Health Organization classification, these tumors are divided into two groups:
- Neuroendocrine tumor (NET) — well differentiated; graded G1, G2 or G3 according to Ki-67 and mitotic count. It generally progresses more slowly and responds to treatments such as somatostatin analogs and PRRT.
- Neuroendocrine carcinoma (NEC) — poorly differentiated and high-grade by definition. It has two subtypes: small cell and large cell. It is aggressive; treatment is platinum-etoposide chemotherapy.
Carcinoma of Unknown Primary
Sometimes metastasis is detected but its source cannot be found. This is called cancer of unknown primary (CUP). Its frequency has decreased as imaging and immunohistochemistry have improved: from 3-5% of all cancers in the 1990s to 1-2% today. Histology is overwhelmingly carcinoma: well/moderately differentiated adenocarcinoma 50%, poorly differentiated adenocarcinoma 30%, squamous cell carcinoma 15%.
Does Molecular Profiling Work? CUPISCO (n=436) tested this: treatment guided by comprehensive genomic profiling extended median PFS compared with chemotherapy to 6.1 months versus 4.4 months (HR 0.72). However, no targetable alteration was found in more than two-thirds of patients. Genomic profiling is therefore now included in guidelines, but the absolute gain is on the scale of weeks to months.
Sarcomatoid Carcinoma: A Misleading Name
Sarcomatoid carcinoma is a carcinoma of epithelial origin that looks like sarcoma under the microscope. This appearance results from a process called epithelial-mesenchymal transition; cytokeratin staining reveals its epithelial origin. It is not a sarcoma. It can occur in the urothelium, kidney (sarcomatoid RCC), lung, prostate, breast (metaplastic carcinoma) and thymus, and has a worse course than conventional carcinoma of the same organ.
How Is Carcinoma Diagnosed?
| Step | What it can and cannot do |
|---|---|
| Laboratory tests | Tumor markers can be measured in blood and urine. They cannot diagnose cancer on their own; they help with follow-up and, in some cases, diagnosis. |
| Imaging | Ultrasound, computed tomography, magnetic resonance, X-rays and PET-CT locate the mass and show its extent. They cannot tell whether the mass is cancer. |
| Biopsy | The only method that establishes the diagnosis. Cell type, grade and immunohistochemistry are assessed in the tissue obtained. For details: What is a biopsy, and how is it performed? |
| Molecular tests | Biopsy material is examined for targetable gene alterations. This can directly change treatment selection. |
The Picture in Turkey
| Rank | Most common in men | Most common in women |
|---|---|---|
| 1 | Lung (24.0%) | Breast (24.5%) |
| 2 | Prostate (14.0%) | Thyroid (14.3%) |
| 3 | Colorectal (9.3%) | Colorectal (8.5%) |
| 4 | Bladder (8.9%) | Uterine corpus (6.5%) |
| 5 | Stomach (6.3%) | Lung (5.6%) |
The estimated number of new cancer cases in Turkey for 2024 is 235,949. What stands out in the table above is that all ten cancers listed are carcinomas —lung, prostate, colorectal, bladder, stomach, breast, thyroid and uterine corpus. No further statistic is needed to understand why carcinoma is so dominant.
Turkey's Free National Screening Program (KETEM)
- Breast: women aged 40-69, mammography every two years.
- Cervix: women aged 30-65, an HPV-DNA test every five years. Turkey is among the countries using HPV-DNA as the primary screening test, an approach ahead of many national programs.
- Colorectal: women and men aged 50-70, a fecal occult blood test every two years, colonoscopy every ten years.
Frequently Asked Questions
- My Pathology Report Says "Carcinoma." What Does That Mean?
- It means the tumor arises from epithelial cells. On its own, this is neither good nor bad news: 80-90% of cancers are carcinomas. The actual determinants appear later in the report: in situ or invasive, which organ, which grade and which stage.
- What Does "In Situ" Mean? Is It Serious?
- It means the cancer cells have not crossed the basement membrane and therefore cannot spread. It is Stage 0, and complete removal usually provides a cure. It must be taken seriously because some cases can become invasive over time, but it is fundamentally different from invasive cancer.
- Is Melanoma a Carcinoma?
- No. Melanoma arises from pigment cells (melanocytes) in the skin; these are not epithelial cells. Basal and squamous cell skin cancers are carcinomas; melanoma is not. Although all three are grouped under "skin cancer," their biology, behavior and treatment differ.
- Which Is Worse: Carcinoma or Sarcoma?
- This is not the right way to frame the question. Both are malignant, and both include very slow-growing and highly aggressive diseases. What matters is not the group but the organ, subtype, grade and stage.
- My Grade Is 3. Does That Mean My Stage Is Also 3?
- No. Grade describes how abnormal the cells look under the microscope; stage describes how far the disease has spread. These are independent measures; both an early-stage high-grade tumor and an advanced-stage low-grade tumor are possible.
- They Could Not Find Where My Cancer Started. Is That Bad?
- Cancer of unknown primary accounts for 1-2% of all cancers and is generally more difficult. However, some patients (approximately 15-20%) belong to subgroups with a more favorable course. Today, comprehensive genomic profiling is recommended; if a targetable alteration is found, treatment is selected accordingly.
- Will I Receive Chemotherapy for Basal Cell Carcinoma?
- Almost certainly not. The vast majority of basal cell carcinomas are treated with surgery. In advanced cases unsuitable for surgery, Hedgehog pathway inhibitors (vismodegib, sonidegib) and immunotherapy (cemiplimab) are used, rather than conventional chemotherapy. Chemotherapy has no established role in this disease.
- I Was Not Given Chemotherapy for Kidney Cancer. Am I Being Undertreated?
- No—this is the correct approach. Renal cell carcinoma is resistant to conventional chemotherapy; a review covering more than 4,000 cases found a response rate of only 6%. Today's standard in metastatic disease is immunotherapy-based combinations, which have increased median survival to over four years.
- Can Carcinoma Be Prevented?
- For a substantial proportion, yes. Stopping smoking (lung, bladder, head and neck), HPV vaccination (cervix, head and neck), hepatitis B vaccination (liver), sun protection (skin), weight control and limiting alcohol have measurable effects. Participation in national screening also offers a chance to detect a tumor before it crosses the basement membrane.
Brief Glossary
- Epithelium
- The cell layer covering the body's internal and external surfaces. The point of origin of carcinomas.
- Basement membrane
- The thin membrane beneath the epithelium. The boundary that cancer must cross to spread.
- Carcinoma in situ
- Carcinoma that has not crossed the basement membrane and therefore cannot spread. Stage 0.
- Invasive carcinoma
- Carcinoma that has crossed the basement membrane and spread into underlying tissue.
- Adenocarcinoma
- Carcinoma arising from secretory glandular epithelium.
- Squamous cell carcinoma
- Carcinoma arising from flat epithelial cells.
- Sarcoma
- A malignant tumor arising from connective tissues such as bone, muscle, fat and cartilage.
- Grade
- A measure of how far cells depart from normal under the microscope. G1 well differentiated, G4 undifferentiated.
- Stage
- The extent of disease. Determined using TNM: T tumor, N lymph node, M distant metastasis.
- Immunohistochemistry
- A method of identifying tumor origin by staining particular proteins in tissue with antibodies.
- Cytokeratin
- A protein family specific to epithelial cells. Positivity is the main basis for a carcinoma diagnosis.
- Cancer of unknown primary (CUP)
- Cancer with detected metastasis but no identified organ of origin.
DROZDOGAN Academy Commentary
This article explains a word patients encounter in their pathology reports, rather than a single disease. We share our own assessment below.
⚡ Why Does This Topic Matter?
Because the most common problem we encounter in the clinic is not a lack of information but incorrectly structured information. A patient arrives with a pathology report and reads "carcinoma"; they do not know what it means but feel the weight of the word. Yet "carcinoma" alone carries almost no prognostic information: 80-90% of cancers are carcinomas.The real information lies later in the report, where two words change everything: "in situ" and "invasive". The difference between them is whether a microscopic membrane has been crossed—and that membrane separates a lesion with a very high chance of cure from a potentially life-threatening disease. If only one thing could be explained to a patient, this would be it.
✅ Strengths / What Is Improving
Some things in this field really have improved in recent years. Pathological diagnosis is much more precise. Thanks to immunohistochemistry and molecular methods, the proportion of cancers of unknown primary has fallen from 3-5% to 1-2% —meaning the source can now be found in more than half of patients previously told that the origin was unknown.Second, terminology is becoming more honest. Replacing "invasive ductal carcinoma" with "invasive carcinoma of no special type" is not cosmetic; the old name implied the wrong biology by suggesting that the tumor arose from a duct cell.
Third, and most importantly in our view: active monitoring is being investigated for DCIS. COMET and LORD show that monitoring low-risk DCIS without surgery is not inferior. Moving toward "less treatment" rather than "more treatment" is rare and valuable in oncology.
⚠️ Limitations / What Should Not Be Overstated
The error rate in Turkish sources is high. Among the things we corrected while preparing this article were "chemical peeling" and "chemotherapy" being presented as treatments for basal cell carcinoma, and radiotherapy and chemotherapy being listed as the main treatments for renal cell carcinoma. These points are not merely incomplete; they are wrong. The chemotherapy response rate in RCC is 6%; this error can lead a patient to worry, "I was not given chemotherapy, so I am being undertreated."Second, the limits of statistics. The "80-90% carcinoma" figure underestimates the true proportion because skin cancers are not recorded. Similarly, the distribution table in this article was derived from US data; for Turkey, a distribution by morphology has not been published.
Third, the power of immunohistochemistry should not be overstated. The CK7/CK20 algorithm looks elegant, but in cancers of unknown primary it can identify the origin in fewer than 30% of cases. A pathology report is a map of probabilities, not a precise address.
Finally, we are cautious about active monitoring in DCIS: follow-up periods are still around two years. DCIS is a lesion that progresses over decades; a two-year "noninferiority" result is not sufficient for a lasting standard.
🩺 Our Position in Practice
- We read the report together with the patient. Explaining "carcinoma" takes five seconds; without an explanation, a patient may live for weeks with the wrong fear.
- If it is "in situ," we emphasize this. This is the best news the patient needs to hear, and it is often lost within the report.
- We state grade and stage separately. When they are confused, patients systematically misjudge their own situation.
- We pursue immunohistochemistry in poorly differentiated tumors. "Adenocarcinoma, uncertain primary" is not an endpoint but an intermediate stop; a decision should not be made before expanding the panel.
- We request genomic profiling in cancer of unknown primary. No targetable finding will emerge in two-thirds of patients, but it makes a difference for the one-third in whom it does.
- We remind patients about screening at every visit. Breast, cervical and colorectal screening is free in Turkey, and our HPV-DNA-based cervical program is ahead of many countries. Not using it means missing the least expensive gain available to us.
❓ Open Questions
Can We Predict Which Cases of DCIS Will Progress? We cannot do so today; that is why all are treated, some unnecessarily. Long-term results from COMET and LORD will bring us closer to an answer. Will the Proportion of Cancers of Unknown Primary Fall to Zero? Methylation profiling and AI-assisted pathology are moving in that direction, but how much knowing the origin changes treatment for patients without a targetable alteration remains debated. And specifically for Turkey: why do we lack cancer statistics by morphology? Our registration system classifies cancers by organ; publishing a breakdown by cell type would be valuable for both research and health planning.Our brief verdict: "Carcinoma" is not a diagnosis but an address—it tells us which cell the cancer arose from, not how dangerous it is. Three things in the pathology report really matter: in situ or invasive, which grade, and which stage. Everything else is shaped around these three questions.
Transparency note. Points that could not be established definitively in this article:
- The article's distribution table by cell of origin is a calculation based on US 2026 cancer estimates, not a single published statistic. The official statement that can be cited is the US National Cancer Institute's "80-90%" range.
- No published data on the proportion of cancers in Turkey that are carcinomas could be found. Turkey's cancer registration system classifies tumors by organ and does not publish a cell-type breakdown.
- Turkey Cancer Statistics 2020 was published in 2025 and covers 50.6% of the population in 14 provinces. Its numerical tables could not be read because they are images. The Turkey figures in this article were therefore taken from IARC GLOBOCAN 2024 data.
- A population-based incidence of nonmelanoma skin cancer for Turkey could not be found; GLOBOCAN does not cover these cancers at all.
- The KETEM screening protocol was verified from two consistent Turkish sources rather than the General Directorate of Public Health's own page. Confirmation from the official source is recommended, especially for the upper age limit of cervical screening.
- No official figure for the percentage of colorectal cancers that are adenocarcinomas could be found; therefore, the phrase "the vast majority" was used.
- LORIS study results have not been published; only COMET and LORD data were used in this article.
- The suffix table (-om, -carcinoma, -sarcoma, -blastoma) is standard pathology textbook information; it was not verified against a single primary source.
- This article is for general information. Review your own pathology report together with your physician; the general information here does not replace individual interpretation.
References
- National Cancer Institute. SEER Training Modules — Cancer Classification. Bethesda, MD
- American Cancer Society. Cancer Facts & Figures 2026. Atlanta; and Siegel RL, et al. Cancer statistics, 2026. CA: A Cancer Journal for Clinicians
- International Agency for Research on Cancer. Global Cancer Observatory — Türkiye fact sheet, 2024
- Republic of Turkey Ministry of Health, General Directorate of Public Health. Turkey Cancer Statistics 2020. Ankara, 2025
- National Cancer Institute. Tumor Grade; and Cancer Staging (TNM)
- Selves J, et al. Immunohistochemistry for diagnosis of metastatic carcinomas of unknown primary site. Cancers 2018;10(4):108
- Rassy E, Pavlidis N. Progress in refining the clinical management of cancer of unknown primary. British Journal of Cancer 2020;122:1123-1132
- Krämer A, et al. Molecularly guided therapy versus chemotherapy after disease control in unfavourable cancer of unknown primary (CUPISCO). Lancet 2024
- Rindi G, et al. Overview of the 2022 WHO classification of neuroendocrine neoplasms. Endocrine Pathology 2022
- NCCN Clinical Practice Guidelines in Oncology: Basal Cell Skin Cancer, 2026; and Squamous Cell Skin Cancer
- Sekulic A, et al. Long-term safety and efficacy of vismodegib in patients with advanced basal cell carcinoma (ERIVANCE BCC final update). BMC Cancer 2017
- Dummer R, et al. Sonidegib in advanced basal cell carcinoma: 42-month analysis of BOLT. British Journal of Dermatology 2020;182(6):1369-1378
- U.S. Food and Drug Administration. Cemiplimab-rwlc approvals: metastatic/locally advanced cutaneous squamous cell carcinoma (28 September 2018), advanced basal cell carcinoma (9 February 2021), adjuvant cutaneous squamous cell carcinoma (8 October 2025)
- Motzer RJ, et al. Nivolumab plus ipilimumab versus sunitinib in advanced renal cell carcinoma (CheckMate 214), 8-year follow-up
- Rini BI, et al. Pembrolizumab plus axitinib versus sunitinib (KEYNOTE-426), 5-year analysis. Nature Medicine 2025
- Choueiri TK, et al. Nivolumab plus cabozantinib versus sunitinib (CheckMate 9ER), final analysis
- National Cancer Institute PDQ. Bladder Cancer Treatment; and EAU Guidelines on Upper Urinary Tract Urothelial Cell Carcinoma
- Hwang ES, et al. Active monitoring with guideline-concordant care in low-risk DCIS (COMET). JAMA 2024
- LORD trial early results. European Breast Cancer Conference 2026
- Fisher B, et al. Tamoxifen in treatment of intraductal breast cancer (NSABP B-24). Lancet 1999
- Turkish Cancer Society and National Cancer Screening Standards. Cancer screening programs in Turkey
Sources
Chun C. and Martin L. (11.06.2020). What is carcinoma? Medical News Today: https://www.medicalnewstoday.com/
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