A New Oncotype Score Addresses Whether Radiotherapy Is Always Needed in DCIS

Ductal carcinoma in situ (DCIS) is described as an early stage of breast cancer in which cancer cells remain confined to the breast ducts. Because the cells have not spread outside the ducts, DCIS is considered noninvasive cancer. It is usually detected through mammography screening and carries a risk of becoming invasive breast cancer if untreated. DCIS has become more common as screening methods have improved and accounts for approximately 20-25% of breast cancer cases. This proportion may vary with advances in screening technology and increased cancer awareness.

What Is the Current Standard Treatment Approach for DCIS?

• Testing estrogen receptor (ER) status is recommended in DCIS to determine the potential risk-reducing benefit of adjuvant endocrine therapy. Testing human epidermal growth factor receptor 2 (HER2) status is not recommended.
• Genetic counseling is recommended for patients at high risk of hereditary breast cancer.
• Breast magnetic resonance imaging (MRI) is recommended only during the initial evaluation.
• Primary Treatment: The primary treatment for DCIS is surgery. Adjuvant (postoperative) radiation therapy (RT) and hormonal therapy are considered afterward. Surgery is currently recommended for all DCIS patients.
• Surgery can involve removing the entire breast (radical mastectomy) or only the area containing the tumor (breast-conserving surgery).
• For DCIS treated with surgery alone, without whole-breast irradiation, a clear surgical margin is important. In these cases, a margin of at least 2 mm of healthy tissue around the removed tissue is recommended. This provides reassurance that all cancerous tissue has been removed and that the likelihood of spread into surrounding healthy tissue is low.
• After Primary Treatment: For ER-positive DCIS treated with breast-conserving surgery (BCS), endocrine therapy containing tamoxifen or an aromatase inhibitor may be considered to reduce the risk of recurrent cancer on the same side. However, the benefit of endocrine therapy in ER-negative DCIS remains unknown.
• Follow-up should include interval history-taking and physical examinations every 6-12 months for 5 years and annually thereafter, plus annual diagnostic mammography. In patients treated with BCT, the first follow-up mammogram should be performed 6-12 months after completing RT. Patients taking endocrine therapy for risk reduction should be monitored according to NCCN guidelines.

The Current Study – Does Every Patient Need Postoperative Radiotherapy?

The Oncotype DX Breast Score is an important genetic test for managing treatment in early-stage hormone-positive breast cancer. It analyzes various genetic biomarkers in a comprehensive model to assess the patient's recurrence risk. This tumor-tissue analysis is also called a recurrence score test.

Oncotype DX is widely used in invasive (conventional) breast cancer to predict disease course and guide treatment decisions. By examining the cancer's biological features, it produces a score providing important information on whether postoperative chemotherapy is needed. Its effectiveness in determining chemotherapy requirements in conventional breast cancer has been scientifically demonstrated. More recently, a version developed for DCIS has begun to be tested to assess radiotherapy needs in these patients.

A new study examined the score's applicability to DCIS treatment. Presented at the 2023 San Antonio Breast Cancer Symposium(SABCS), it found that the Oncotype DX Breast DCIS Score could effectively identify low-risk patients who do not need adjuvant radiotherapy after surgery. This could help avoid unnecessary treatment and offer more personalized options.

The study found that the Oncotype DX score helped identify patients at low and high risk of DCIS recurrence. After breast-conserving surgery (BCS), some patients classified as low risk omitted adjuvant radiotherapy and had similar 5-year recurrence rates to high-risk patients receiving radiotherapy. This finding demonstrates the score's accuracy in identifying low-risk patients.

This is the first prospective study evaluating radiation decisions in DCIS patients.

Study Details

The study included 171 DCIS patients who underwent breast-conserving surgery and whose MRI confirmed that more extensive surgery was unnecessary. Surgical specimens were tested using the 12-gene Oncotype DX test to determine the DCIS score.

On the 100-point Oncotype DX scale,

• women scoring <39 were considered at low risk of recurrence and advised to avoid radiation.
• Women scoring >39 were advised to receive radiotherapy.

93% of patients followed the radiation recommendations:

• Of the 82 patients classified as low risk, 75 (91.4%) avoided adjuvant radiotherapy as recommended, and
• Of the 89 classified as high risk, 84 (94.4%) received radiotherapy.

At a median follow-up of 5 years, 5.1% of low-risk patients (four of 82) experienced recurrence, compared with 4.5% of higher-risk patients (four of 89).

Recurrence rates among patients following the radiation recommendations reflected these overall findings:

• Among 75 low-risk DCIS patients who avoided radiotherapy, 5.5% experienced recurrence, whereas
• Among 84 high-risk patients receiving radiotherapy, 4.8% experienced recurrence.

Age did not appear to affect outcomes. Two of the 33 women younger than 50 experienced recurrence (4%), both as invasive, conventional breast cancer. One was in the low-risk group and the other in the higher-risk group. Six of the 138 older women experienced recurrence, three in each group; one patient in each group had invasive cancer recurrence.

In summary, the score successfully identified low-risk DCIS patients. Women who avoided radiation based on the score did not experience excessive ipsilateral (same-side) recurrence risk within 5 years.

Overall, the study provides “strong evidence that may help avoid overtreatment for some patients,” although the score's success will become clearer with 10-year follow-up results.