Increased risk of MDS/AML post radiation treatment for breast cancer: Analysis of SEER data 2001-2008.

Abstract

6560 Background: Ionizing radiation is a known cause of myeloid leukemia, but it is not known whether therapeutic doses for breast cancer (BC) pose 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 institutional cohort study. Methods: We used 2001-2008 Surveillance, Epidemiology and End Results (SEER) database records to identify a cohort of first primary BC patients treated with radiation who were unlikely to be treated with chemotherapy (stage 0 and estrogen receptor positive (ER+) stage I). We identified subsequent MDS/AML diagnoses in the BC cohort, using SEER to query appropriate ICD-O-3 codes. We compared observed MDS/AML rates in the BC cohort to expected rates, estimated for first primary MDS/AML in the entire population, and calculated observed/expected rate ratios with 95% confidence intervals (CI). Results: We estimated an increased overall risk of MDS/AML in the breast cancer cases treated with radiation compared to the general population (RR=4.23, 95% CI 3.41, 5.18). The relative risk was higher for stage I ER+ breast cancer cases <65 years of age (RR=7.75, 95% CI 5.18, 11.05) than for stage 0 cases <65 years of age (RR=3.65, 95% CI 1.57, 7.05). Among women 65 years and older, there was a more modest increased risk, only seen for stage 1 ER+ breast cancer cases (RR=1.52) (table). Conclusions: Our results suggest that radiation treatment for breast cancer is associated with increased risk of MDS/AML. The effect appears to be age-dependent. [Table: see text]