International Journal of Radiation Oncology*Biology*Physics
Clinical investigation: breastSarcoma as a second malignancy after treatment for breast cancer
Introduction
Radiotherapy (RT) is considered a risk factor in breast cancer patients for the development of soft-tissue and bone sarcomas 1, 2, 3, 4, 5. Because of the low incidence of sarcomas, the absolute level of risk is not known with certainty. Prior studies examining radiation-associated sarcoma in breast cancer patients have been based on relatively small numbers of cases. Nonetheless, with new indications for RT and increased screening, more and younger patients are having multimodality treatment (including radiotherapy) for breast cancer (6). Using Surveillance, Epidemiology and End Result (SEER) data (7), we attempted to better define risk levels and the impact of radiation therapy on the development of sarcoma in women previously diagnosed as having breast cancer. Of major interest were the histologies encountered, the cumulative incidence rates, and the latency periods for sarcomas occurring with or without radiotherapy given as part of breast cancer treatment.
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Methods and materials
Women having a diagnosis of invasive breast cancer were identified (n = 274,572) in the SEER Cancer Incidence Public-Use Database, 1973–1996 (7). Excluded from the analysis were cases initially identified based on autopsy reports or death certificates, cases for which breast cancer was diagnosed as a subsequent malignant neoplasm, and male breast cancers. Mixed mullerian tumor and carcinosarcoma were excluded from our classification as secondary sarcomas. The database was then queried to
Results
The characteristics of primary breast cancer cases studied are shown in Table 1. Of the 274,572 cases of invasive breast cancer identified in the SEER database 1973–1997, 82,296 (30%) received radiation therapy, and 192,276 (70%) did not receive radiation therapy. In 5,232 cases, it was unknown whether patients received radiation therapy; these were excluded from analysis. Few breast cancers were diagnosed in patients under the age of 20 (n = 23), and only about 7% of patients were aged 20–39
Discussion
Ionizing radiation is known to be a potent carcinogen (12); malignancy induced by radiation may result from natural sources or a radiation accident, or it may be a side effect of cancer therapy (13). Solid cancers associated with exposure to ionizing radiation may have latency periods of up to 40 years (13). Approximately 6.7% of new cancers represent second primary cancers in cancer survivors (14), and breast cancer survivors constitute up to 25% of all cancer survivors 15, 16. In addition to
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