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Annual Meeting Proceedings Part 1 - American Society of Clinical ...

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6560 General Poster Session (Board #17C), Mon, 1:15 PM-5:15 PM<br />

Increased risk <strong>of</strong> MDS/AML post radiation treatment for breast cancer:<br />

Analysis <strong>of</strong> SEER data 2001-2008. Presenting Author: Henry G. Kaplan,<br />

Swedish Cancer Institute, Seattle, WA<br />

Background: Ionizing radiation is a known cause <strong>of</strong> myeloid leukemia, but it<br />

is not known whether therapeutic doses for breast cancer (BC) pose risk. We<br />

hypothesized that BC radiation treatment is associated with increased risk<br />

<strong>of</strong> myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML))<br />

as seen in a previously conducted institutional cohort study. Methods: We<br />

used 2001-2008 Surveillance, Epidemiology and End Results (SEER)<br />

database records to identify a cohort <strong>of</strong> first primary BC patients treated<br />

with radiation who were unlikely to be treated with chemotherapy (stage 0<br />

and estrogen receptor positive (ER�) stage I). We identified subsequent<br />

MDS/AML diagnoses in the BC cohort, using SEER to query appropriate<br />

ICD-O-3 codes. We compared observed MDS/AML rates in the BC cohort to<br />

expected rates, estimated for first primary MDS/AML in the entire population,<br />

and calculated observed/expected rate ratios with 95% confidence<br />

intervals (CI). Results: We estimated an increased overall risk <strong>of</strong> MDS/AML<br />

in the breast cancer cases treated with radiation compared to the general<br />

population (RR�4.23, 95% CI 3.41, 5.18). The relative risk was higher for<br />

stage I ER� breast cancer cases �65 years <strong>of</strong> age (RR�7.75, 95% CI<br />

5.18, 11.05) than for stage 0 cases �65 years <strong>of</strong> age (RR�3.65, 95% CI<br />

1.57, 7.05). Among women 65 years and older, there was a more modest<br />

increased risk, only seen for stage 1 ER� breast cancer cases (RR�1.52)<br />

(table). Conclusions: Our results suggest that radiation treatment for breast<br />

cancer is associated with increased risk <strong>of</strong> MDS/AML. The effect appears to<br />

be age-dependent.<br />

Expected and observed MDS/AML incidence rates in breast cancer cases<br />

with radiation treatment (per 100,000 person years).<br />

Expected<br />

rate<br />

Person<br />

years<br />

Observed rate<br />

(n�cases)<br />

Rate ratio<br />

(95% CI)<br />

Stage 0, age

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