Impact of radiation therapy and/or chemotherapy on the risk for a second malignancy after breast cancer

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Abstract
The risk of any second malignancy was determined for all patients treated for a primary cancer of the breast without evidence of distant metastasis at Duke University Medical Center between 1970 and 1981. The incidence, 10-year actuarial risk (AR), and relative risk (RR) of a second malignancy developing were calculated for the 407 patients who were treated with surgery alone, 226 who were treated with surgery followed by adjuvant chemotherapy (CT), 140 who were treated with surgery plus adjuvant radiation therapy (RT), and 308 who received all three modalities (CRT). The AR of a subsequent cancer (8.4% for CRT, 8.7% for CT, 8.7% for RT, and 11.7% for surgery only patients) did not differ significantly between treatment groups. The overall second cancer RR was 1.0% after CRT (95% confidence interval [CI], 0.4 to 2.0), 1.3% after RT (95% CI, 0.6 to 2.5), 1.6% after CT (95% CI, 0.9 to 2.6), and 1.7% after surgery alone (95% CI, 1.2 to 2.4). Contralateral breast cancers (RR of 4.2%; 95% CI, 2.7 to 6.3) account for the statistically significant excess of second malignancies among the surgery alone patients. The AR for contralateral breast cancer in the surgery group was higher than in either group receiving CT (P < 0.01), but was not significantly different from the RT group. The RR for solid tumors other than breast cancer was not significantly different from unity in any of the treatment groups. The RR for acute leukemia was 16.7% in the CRT group (95% CI, 0.2 to 92.7), 11.1% in the CT group (95% CI, 0.1 to 61.8), 10.0% in the surgery alone group (95% CI, 1.1 to 36.1), and 0.0% in the RT group (95% CI, 0.0 to 61.1). This study indicated that inclusion of RT and/or CT in the initial treatment of breast cancer did not impact negatively on patients' overall risk for a subsequent malignancy during the first decade after therapy, and that adjuvant CT with or without RT may decrease their risk of a contralateral breast cancer.