Influence of hormone replacement therapy on tamoxifen-induced vasomotor symptoms

Tamoxifen is an effective drug, but its role in prevention is limited by its adverse effect profile. Non-life-threatening adverse effects, such as vasomotor symptoms, have an important influence in its use for prevention. Vasomotor symptoms were evaluated according to follow-up time, severity, and use of hormone replacement therapy (HRT) in a retrospective analysis.

In the International Breast Cancer Intervention Study-I study, 7,154 women at increased risk of breast cancer were randomly assigned to either tamoxifen 20 mg/d or placebo for 5 years. Women gave detailed information on any vasomotor symptoms at each 6-month follow-up visit.

Hot flushes were reported more often in the tamoxifen group than in the placebo group (70.6% v 57.1%, respectively; odds ratio, 1.80; 95% CI, 1.63 to 1.99). Severe hot flushes were more strongly related to tamoxifen. In the tamoxifen arm, more women taking HRT at entry experienced hot flushes in the first 6 months than those who did not take HRT (60.8% v 49.2%, respectively; P = .09). In contrast, women on placebo taking HRT at entry experienced fewer hot flushes than women who stopped HRT (22.9% v 34.3%, respectively; P = .03). Furthermore, for women who first began HRT in the first 6 months of the trial compared with women who did not begin HRT, HRT seemed to be much more effective in controlling hot flushes in months 6 to 12 in the placebo arm (47.9% v 20.4%, respectively) than in the tamoxifen arm (51.4% v 39.0%, respectively).

HRT use at entry or during the trial was not effective in alleviating hot flushes for women in the tamoxifen arm. Our retrospective study suggests that estrogen-based HRT has limited effectiveness among women receiving tamoxifen.