Hormone replacement therapy is not associated with an increased risk of leukemia (United States)

Objective: Recent studies have reported an increased risk of certain cancers associated with hormone replacement therapy (HRT), possibly due to stimulation of estrogen receptors. Since estrogen receptors are expressed on certain hematopoietic cells, it is possible that HRT use may also increase the risk of leukemia. Methods: A cohort of 37,172 post-menopausal Iowa women ages 55-69 years with no history of prior cancer was linked annually to the population-based state cancer registry through 2001. In addition to other self-reported cancer risk factors, participants were asked about current and former use of HRT in 1986 and on four subsequent follow-up questionnaires. A total of 201 cases of leukemia were identified over 16 years of follow-up including 74 acute myeloid leukemias (AMLs) and 87 chronic lymphocytic leukemias (CLLs). Results: Compared to never users of HRT at study baseline, current [multivariate relative risk (RR), 1.09; 95% confidence interval (CI) 0.70-1.71)] and former users (RR=0.82, 95% CI=0.59-1.15) were at no increased risk of developing leukemia. For AML, current users also had no increased risk (RR=0.83, 95% CI=0.37-1.84) and there was a suggestion that former users had a slightly decreased risk (RR=0.66, 95% CI=0.37-1.17). For CLL, all RRs were around unity. Conclusion: We conclude that HRT is unlikely to be an appreciable risk factor for leukemia.