Acute myeloid leukemia after adjuvant breast cancer therapy in older women: understanding risk.

PURPOSE: The purpose of this study was to determine the risk of developing acute myeloid leukemia (AML) after adjuvant chemotherapy for breast cancer in older women.

PATIENTS AND METHODS: Data from the Surveillance, Epidemiology, and End Results-Medicare linked database were used for women diagnosed with nonmetastatic breast cancer from 1992 to 2002. The primary end point was a claim with an inpatient or outpatient diagnosis of AML (International Classification of Diseases ninth revision, codes 205 to 208), comparing patients treated with and without adjuvant chemotherapy, and by differing chemotherapy regimens. The cumulative hazard of AML was estimated using the Kaplan-Meier method. Cox proportional hazards models were used to determine factors independently associated with the development of AML.

RESULTS: In this observational study, there were 64,715 patients: 10,130 received adjuvant chemotherapy and 54,585 did not. The median patient age was 75.6 years (range, 66 to 104 years). The mean follow-up was 54.8 months (range, 13 to 144 months). The absolute risk of developing AML at 10 years after any adjuvant chemotherapy for breast cancer was 1.8% versus 1.2% for women who had not received chemotherapy. The adjusted hazard ratio for AML with adjuvant chemotherapy versus none was 1.53 (95% CI, 1.14 to 2.06). Granulocyte colony-stimulating factor (G-CSF) within the first year of diagnosis did not convey a significantly increased risk of AML (hazard ratio, 1.14; 95% CI, 0.67 to 1.92).

CONCLUSION: There is a small but real increase in AML after adjuvant chemotherapy for breast cancer in older women. This study may underestimate the true incidence because myelodysplastic syndrome cannot be identified through claims. G-CSF use within the first year of diagnosis does not convey an increased risk of AML in older women.