Estrogen Replacement Therapy (ERT) Is Not Associated with an Increased Risk of Leukemia.

Recent studies have reported an increased risk of breast, endometrial, ovarian, and gall bladder cancer associated with ERT. One proposed mechanism by which ERT increases risk is through the binding of estrogen to receptors at the tissue site. Estrogen receptors are also present on certain hematopoietic cells as well as on myeloid leukemia cells. Further, downregulation of the estrogen receptor through DNA methylation has been associated with increased acute myeloid leukemia (AML) survival. We evaluated whether ERT is associated with an increased risk of leukemia, particularly AML, in the Iowa Women’s Health Study. A cohort of 37,172 post-menopausal Iowa women ages 55 to 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 ERT 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 64 AMLs and 87 chronic lymphocytic leukemias (CLLs). Compared to never users of ERT at study baseline, current [multivariate relative risk (RR), 1.09; 95% Confidence Interval (CI) 0.70–1.72) and former users (RR=0.81, 95% CI=0.58–1.14) were at no increased risk of developing leukemia. For AML, current users also had no increased risk (RR=0.86, 95% CI=0.39–1.92) and there was a suggestion that former users had a slight decreased risk (RR=0.68, 95% CI=0.38–1.22). For CLL, all results were around unity. Duration of ERT or time-dependent use had no appreciable effect on the RRs. We conclude that ERT use is unlikely to be a risk factor for leukemia, including AML. Supported by NCI R01 CA39741.