A new study has reported that radiotherapy reduces the risk of local recurrence of ductal carcinoma in situ (DCIS), especially for women with close surgical margins. Surgery for DCIS is not always followed by radiation treatment despite studies reporting its benefit in reducing the risk of ipsilateral breast cancer recurrence (i.e., recurrence in the same breast that was treated). The study included 294 patients with DCIS treated either with surgery alone or with surgery plus radiation between 1991 and 1995. Margin width, number of involved ducts at closest margin, presence of palpable mass, presence of lobular neoplasia, nuclear grade, necrosis, and age were examined individually and in combination as potential factors influencing risk of ipsilateral breast cancer recurrence. The potential addition benefit of radiation treatment was also assessed.

During a median follow-up period of 11 years, an actuarial 10-year ipsilateral breast cancer recurrence rate of 22% was found in the study group overall. The 15-year rate was 29%. For lesions excised with margins of less than 1 mm, 1 to 9 mm, and at least 10 mm, the actuarial 10-year ipsilateral breast cancer recurrence rates were 28%, 21%, and 19%, respectively. Radiation treatment reduced these recurrence rates by 62% for all patients in the study, 83% for lesions with less than 1 mm margins, 70% for 1 to 9 mm, and 24% for margins of at least 10 mm. After adjusting for other variables, higher volume of disease near the surgical margin was found to be associated with more than three times greater risk of ipsilateral breast cancer recurrence in the no radiation treatment group. The authors conclude that the effect of radiation treatment on ipsilateral breast cancer recurrence risk is influenced both by margin width and number of involved ducts at nearest margin. Patients with higher volume of disease near the margin derive the greatest benefit from radiation. However, even in patients with surgical margins of at least 10 mm, the risk of breast cancer recurrence in the treated breast remains substantial in patients with DCIS.