Early results from the WHI study in 2002 caused the study’s intervention phase to be stopped early due to an increased risk of breast cancer among the participants taking HRT, compared to those taking a placebo.
Clinical visits and follow-up continued through March 2005. The study was then extended and recorded any additional new cases of breast cancer beginning in April 2005 and ending in August 2009.
Researchers analyzed data based on 11 years of follow-up of 12,788 women in the original WHI study. They found that HRT was associated with an increased risk of breast cancer; the participants’ cancers were more commonly diagnosed in an advanced stage.
The researchers also found that more than twice as many women who took hormone replacement therapy died within the follow-up period, compared with those who took the placebo (25 vs. 12 deaths, respectively).
The study results are published in TheJournal of the American Medical Association.
"Now, with longer follow-up results available, there remains a cumulative, statistically significant increase in breast cancers in the combined hormone therapy group, and the cancers more commonly had lymph node involvement," write researcher Rowan T. Chlebowski, MD, PhD, of Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, Calif., and colleagues.
In an editorial that accompanies the study, Peter B. Bach, MD, of Memorial Sloan-Kettering Cancer Center in New York, warns that the study does not address the effect of short periods of hormone replacement therapy on breast cancer risk or other long-term complications.
Bach states that additional studies are needed to specifically determine if lower doses or shorter durations of HRT can reduce menopausal symptoms without increasing cancer risk.