Survival and chemotherapy-related risk of second primary malignancy in breast cancer patients: a SEER-based study

Background With the improvement in the survival of breast cancer, developing second primary malignancy becomes a serious health issue. The aim of this study was to explore the survival of breast cancer patients with second primary malignancy, and to evaluate the impact of chemotherapy on the risk of different cancer sites. Method Obtaining data from the Surveillance, Epidemiology, and End Results database, we calculated the standardized incidence ratio (SIR) for second primary malignancy in breast cancer survivors between 2000 and 2014. Overall survival and cancer-specific survival were analyzed with Kaplan-Meier method. Then, we further conducted stratified sub-analyses according to chemotherapy. Results The overall risk of second primary cancer for all sites was significantly elevated in breast cancer patients (SIR=1.15, 95% CI 1.14-1.16). Overall survival and cancer-specific survival of the patients with breast cancer only were significantly better than the patients with multiple primary cancers (both P<0.001). Chemotherapy was associated with increased incidences for all sites, except lymphoma, myeloma, and chronic lymphocytic leukemia (SIR=0.80, 95% CI 0.72-0.88; SIR=0.85, 95% CI 0.71-1.01; SIR=0.57, 95% CI 0.43-0.74, respectively). The risk for developing second acute myeloid leukemia after chemotherapy in breast cancer patients varied with age and latency. Conclusion Female breast cancer patients showed higher incidence of second primary malignancy, which was associated with poorer prognosis. Chemotherapy benefits should be weighed against the risks of second primary malignancy.