A new US study found that women taking combined hormone therapy had an increased risk of otherwise avoidable abnormal mammograms and breast biopsies that compromised the ability of these two methods to help diagnose breast cancer.

The study was carried out by lead author Dr Rowan T Chlebowski, an investigator at the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center (LA BioMed), and colleagues, and is published in the 25th February issue of the Archives of Internal Medicine.

In a press statement Chlebowski said 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, wrote the researchers in their background information to the article.

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 a day and medroxyprogesterone acetate at 2.5 mg a day).

The women underwent mammogram and breast exams at the start 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.

They found that:

  • The hormone group had a higher frequency of mammograms with abnormalities compared with the placebo group (35 versus 25 per cent).
  • Women in the hormone group had a 4 per cent greater risk of having a mammogram with abnormalities after one year and this risk was 11 per cent 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 per cent.
  • Breast cancers were significantly increased and diagnosed at higher stages in the hormone group.
  • But despite this, biopsies in the hormone group diagnosed cancer less frequently compared with the placebo group (14.8 versus 19.6 per cent).
  • When hormone therapy was stopped, the adverse effect on mammograms remained significantly different to that of placebo for at least 12 months after.

Chlebowski and colleagues concluded that:

“Use of conjugated equine estrogens plus medroxyprogesterone acetate for approximately 5 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.”

They added that:

“This adverse effect on breast cancer detection should be incorporated into risk-benefit discussions with women considering even short-term combined hormone therapy.”

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 said 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.”

“Estrogen Plus Progestin and Breast Cancer Detection by Means of Mammography and Breast Biopsy.”
Rowan T. Chlebowski; Garnet Anderson; Mary Pettinger; Dorothy Lane; Robert D. Langer; Mary Ann Gillian; Brian W. Walsh; Chu Chen; Anne McTiernan; for the Women’s Health Initiative Investigators.
Arch Intern Med. 2008;168(4):370-377.
Vol. 168 No. 4, February 25, 2008.

Click here for Abstract.

Sources: Article abstract, LA BioMed press release.

Written by: Catharine Paddock, PhD