Hormone Therapy Found to Compromise Breast Cancer Diagnosis

Rowan T. Chlebowski, an investigator at the Los Angeles Biomedical Research Institute at Harbor-University of Los Angeles, California (UCLA) Medical Center (LA BioMed), and colleagues, and was published in the February 25, 2008, issue of the journal Archives of Internal Medicine.

Dr. Chlebowski reported that the findings "represent a concern for post-menopausal women who are considering hormone therapy.” The effect of combined hormone therapy on the detection of breast cancer has not been determined before, according to the investigators.

Dr. Chlebowski and colleagues studied 16,608 women enrolled in the 15-year Women's Health Initiative (WHI) clinical trial that started in 1993. The women were randomly assigned to two treatment groups: a hormone group and a placebo group. The hormone group received a combination of estrogen and progestin (equine estrogens at 0.625 mg per day and medroxyprogesterone acetate at 2.5 mg per day). The women underwent mammogram and breast exams at the beginning of the trial and annually thereafter. Breast biopsies were also performed if indicated from the clinical findings. The team then looked at the effect of the combined hormones on breast cancer detection over 5.6 years.

The findings of their study revealed that the hormone group had a higher frequency of mammograms with abnormalities compared with the placebo group (35 versus 25%). Women in the hormone group had a 4% greater risk of having a mammogram with abnormalities after one year and this risk was 11% after five years, compared to the women in the placebo group. There was a lower sensitivity for breast cancer detection and increased cumulative frequency of breast biopsy in the hormone group (10.0 versus 6.1%). Breast tumors were considerably increased and diagnosed at higher stages in the hormone group. Despite this, biopsies in the hormone group diagnosed cancer less frequently compared with the placebo group (14.8 versus 19.6%). When hormone therapy was stopped, the adverse effect on mammograms remained significantly different to that of placebo for at least 12 months after.

Dr. Chlebowski and colleagues concluded that "use of conjugated equine estrogens plus medroxyprogesterone acetate for approximately five years resulted in more than 1 in 10 and 1 in 25 women having otherwise avoidable mammogram abnormalities and breast biopsies, respectively, and compromised the diagnostic performance of both. This adverse effect on breast cancer detection should be incorporated into risk-benefit discussions with women considering even short-term combined hormone therapy.”

Dr. Chlebowski advised women considering hormone therapy to "take the results of this study into consideration and consult with their physicians before undergoing even short-term hormone therapy.”

He stated that the results were relevant for women just entering the menopause as well: "After discontinuation of combined hormone therapy, the adverse effects on mammogram and breast biopsy performance were seen even in younger women in the fifth decade of life.”


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Los Angeles Biomedical Research Institute