Prospective Evaluation of Breast-Conserving Surgery Alone in Low-Risk Ductal Carcinoma in Situ (DCIS)

A prospective cohort study, conducted in Canada, to prospectively evaluate whether the combination of clinicopathological criteria and the Oncotype DX DCIS score can identify a group of women at very low risk of local recurrence following breast conserving surgery who do not require breast radiation therapy. We plan to screen 809 consenting women who will have their tumour tissue specimen sent to Exact Sciences to assess their DCIS score. We anticipate that 526 women will have an Oncotype DX DCIS score with a predicted 10-year risk of local recurrence ≤10%, these women will be enrolled and followed as part of the study.

At each centre, all patients with DCIS referred to radiation oncology will be documented. When a physician identifies an eligible patient, the patient will be approached by the referring physician or delegate to voluntarily provide informed consent to participate in this study. Consenting patients will be registered through the Ontario Clinical Oncology Group's (OCOG) web-based registration system. A two-step registration/enrollment process will be implemented.

Data related to the patient demographics, surgery details, tumour characteristics and ECOG performance will be collected. The patient's tumour specimen will be sent for analysis to Exact Sciences. The DCIS score results will be sent to the referring physician. OCOG will also receive the DCIS score results. Patients will be followed yearly up to 10 years. Bilateral mammograms and breast exams will be performed annually. The study data will be verified by source documentation.

Inclusion criteria

• Female patient > 45 years of age with DCIS without microinvasion.
• Tumour size ≤ 2.5cm.
• Treated by BCS with clear resection margins ≥ 2 mm or no residual disease on re-excision.*

• Patients with anterior margins and posterior margins ≥1 mm are eligible. Or if the dissection was confirmed to be taken to skin and down to fascia with no DCIS present at inked margins.
• Oncotype DX DCIS score with a predicted 10-year risk of LR ≤10%.

Exclusion criteria

• Multifocal DCIS.
• History of any invasive breast cancer or non-invasive breast cancer in the ipsilateral breast.
• Synchronous or previous invasive or non-invasive breast cancer.
• Prior history of invasive cancer within the last 5 years, excluding non-melanoma skin cancers.
• ECOG performance status ≥3.
• Life expectancy <10 years.
• Geographic inaccessibility for follow-up.