Extended follow-up on women in a trial that had been halted early found that use of hormone replacement therapy in breast cancer survivors continued to be associated with an increased risk of new breast cancer, researchers report in the April 2 issue of the Journal of the National Cancer Institute.

Lars Holmberg, M.D., Ph.D., of Uppsala University in Sweden, and colleagues report on additional findings from the HABITS study, which ended in 2003 after an increased risk was found for breast cancer recurrence with hormone therapy compared with recurrence without hormone therapy. In the new study, they further analyzed data on 442 of the women who had been randomized to hormone therapy or no hormone therapy.

The researchers report that after a median of four years of follow-up, 39 of the women in the hormone therapy group had a new breast cancer event, compared to 17 in the control arm (hazard ratio 2.4). The cumulative incidence of a new event at five years was estimated at 22.2 percent in the hormone therapy group and 8 percent in the control group.

"Although randomized data concerning use of hormone replacement therapy for symptomatic intervention in breast cancer survivors are still sparse, it seems that the harmful side effects of hormone replacement therapy have finally been clearly demonstrated in what is, by today's standards, a small randomized trial, carried out in a few relatively small countries," writes Kathleen I. Pritchard, M.D., of the Sunnybrook Odette Cancer Centre in Toronto, Ontario, Canada, in an accompanying editorial.

The study was supported by Novo Nordic Pharma with an unrestricted grant.

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