Risk of myelodysplastic syndrome and acute myeloid leukemia post radiation treatment for breast cancer: a population-based study.

Ionizing radiation is a known cause of myeloid leukemia, but it is not known whether therapeutic doses for breast cancer (BC) pose an increased risk. We hypothesized that BC radiation treatment is associated with increased risk of myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) as seen in a previously conducted study. We used 2001-2009 Surveillance, Epidemiology, and End Results (SEER) database records to identify a cohort of women with first primary stage 0 BC who were treated with radiation, a group which is not treated with chemotherapy. We identified subsequent MDS/AML diagnoses in the cohort using SEER to query appropriate ICD-O-3 codes. We compared observed MDS/AML rates in the BC cohort to expected rates, estimated as first primary MDS/AML in the entire female population, and calculated observed/expected rate ratios with 95 % confidence intervals (CI). Overall, a very small number of cases of MDS/AML occurred in this cohort with 22 observed cases versus 9.4 expected cases using national incidence data. We estimated an increased risk of 2.34 for MDS/AML in stage 0 BC cases treated with radiation compared to the general population (95 % CI 1.49, 3.46, p < 0.001). The age adjusted relative risk is 1.46, (95 % CI 0.93, 2.16, p = 0.08). Our results suggest that radiation treatment for BC is associated with an increased risk of MDS/AML and affects a very small number of patients.