Abstract

In 1997 two independent randomized clinical trials, Hormonal Replacement Therapy After Breast Cancer--Is It Safe? (HABITS; 434 patients) and the Stockholm trial (378 patients), were initiated in Sweden to compare menopausal hormone therapy with no menopausal hormone therapy after diagnosis of early-stage breast cancer. Much of the design of both studies was similar; however, a goal of the Stockholm protocol, not shared with the HABITS trial, was to minimize the use of progestogen combined with estrogen. The HABITS trial was prematurely stopped in December 2003, because, at a median follow-up of 2.1 years, the risk for recurrence of breast cancer among patients receiving menopausal hormone therapy was statistically significantly higher (relative hazard [RH] = 3.3, 95% confidence interval [CI] = 1.5 to 7.4) than among those receiving no treatment. In the Stockholm trial, however, at a median follow-up of 4.1 years, the risk of breast cancer recurrence was not associated with menopausal hormone therapy (RH = 0.82, 95% CI = 0.35 to 1.9). Statistically significant heterogeneity in the rate of recurrence was observed (P = .02; two-sided likelihood-ratio test) between the two studies, indicating that chance may not be the only explanation. Doses of estrogen and progestogen and treatment regimens for menopausal hormone therapy may be associated with the recurrence of breast cancer.