Previous studies have shown that HRT increases breast cancer incidence in healthy women, but its impact on breast cancer survivors has remained obscure. Observational studies and one small randomized trial had suggested that HRT had no effect or even might reduce recurrence. However, two-year follow-up data from the randomized HABITS trial indicated that survivors who took HRT were more likely to suffer disease recurrence than those who did not take HRT.
In the current analysis, Lars Holmberg, M.D., Ph.D., currently at King’s College London and his mostly Scandinavian colleagues examined the breast cancer rates for women in the HABITS trial after a median follow-up of four years. At the time of this analysis, 39 (17.6 percent) of the 221 women in the HRT treatment arm had developed breast cancer recurrence or a new breast cancer malignancy, compared with 17 (7.7 percent) of 221 women in the control arm. The estimated five-year cumulative rate for disease recurrence was 22.2 percent for the HRT arm and 9.5 percent in the control arm, for an absolute increase in risk of 14.2 percent.
“The results of the HABITS trial indicate a substantial risk for a new breast cancer event among breast cancer survivors using [HRT]. The risk elevation is in line with the evidence from observational studies and randomized trials that [HRT] increases the risk of breast cancer in healthy women,” the authors write.
Kathy I. Pritchard, M.D., of the Sunnybrook Odette Cancer Center in Toronto discusses the results of the HABITS trial and the Women’s Health Initiative trial in the context of the much less worrisome findings from observational studies. “Although randomized data concerning use of HRT for symptomatic intervention in breast cancer survivors are still sparse, it seems that the harmful side effects of HRT have finally been clearly demonstrated,” Pritchard writes.
MEDICA.de; Source: Journal of the National Cancer Institute