Sarcoma as a second malignancy after treatment for breast cancer.

BACKGROUND: Second malignant neoplasms may be a consequence of radiotherapy for the treatment of breast cancer. Prior studies evaluating sarcomas as second malignant neoplasms in breast cancer patients have been limited by the numbers of patients and relatively low incidence of sarcoma. Using data from the Surveillance, Epidemiology and End Results registries, we evaluated the influence of radiation therapy on the development of subsequent sarcomas in cases with primary breast cancer.
METHODS: Cases with primary invasive breast cancer (n = 274,572) were identified in the Surveillance, Epidemiology and End Results Cancer Incidence Public-Use Database (1973-1997). The database was then queried to determine the cases developing subsequent sarcomas (n = 263). Eighty-seven of these cases received radiation therapy, and 176 had no radiation therapy. The cumulative incidence of developing secondary sarcoma and the survival post developing secondary sarcoma were determined by the Kaplan-Meier method.
RESULTS: The occurrence of sarcoma was low, regardless of whether cases received or did not receive radiation therapy: 3.2 per 1,000 (SE [standard error] = 0.4) and 2.3 per 1,000 (SE = 0.2) cumulative incidence at 15 years post diagnosis, respectively (p = 0.001). Of the sarcomas occurring within the field of radiation, angiosarcoma accounted for 56.8%, compared to only 5.7% of angiosarcomas occurring in cases not receiving radiotherapy. The cumulative incidence of angiosarcoma at 15 years post diagnosis was 0.9 per 1,000 for cases receiving radiation (SE = 0.2) and 0.1 per 1,000 for cases not receiving radiation (SE < 0.1). Overall survival was poor for cases of sarcoma after breast cancer (27-35% at 5 years), but not significantly different between patients receiving or not receiving radiation therapy for their primary breast cancer.
CONCLUSIONS: Radiotherapy in the treatment of breast cancer is associated with an increased risk of subsequent sarcoma, but the magnitude of this risk is small. Angiosarcoma is significantly more prevalent in cases treated with radiotherapy, occurring especially in or adjacent to the radiation field. The small difference in risk of subsequent sarcoma for breast cancer patients receiving radiotherapy does not supersede the benefit of radiotherapy.