According to a study published March 15 in the Journal of the National Cancer Institute, thoughts about how estrogen alone or estrogen in addition to progestin influence the risk of developing breast cancer has considerably changed in the past 10 years due to results from the Women’s Health Initiative (WHI) randomized placebo-controlled hormone therapy trials, and from large prospective cohort studies.
At present, concerns are still being raised regarding hormone therapy-induce breast cancer risk, even though the therapy is used for menopausal symptoms by millions of women. Furthermore, researchers are still not clear on the effects of estrogen in addition to progestin vs estrogen alone on breast cancer.
Rowan T. Chlebowski, M.D., Ph.D., of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center and Garnet Anderson, Ph.D., at Fred Hutchinson Cancer Research Center, examined data from 2 randomized, placebo-controlled clinical trials carried out in the WHI, in order to examine the effects of estrogen in addition progestin vs estrogen alone on the risk of developing breast cancer.
The first study assessed estrogen alone in post-menopausal women with prior hysterectomy, and the second study assessed estrogen plus progestin in post-menopausal women who had not undergone hysterectomy.
The researchers found that the risk of developing breast cancer was statistically considerably increased by using estrogen in addition to progestin, while the risk was statistically significantly decreased in post-menopausal women with previous hysterectomy who took estrogen alone.
According to the researchers, findings from the randomized human trial and those from the majority of observational studies differ, with the observational studies indicating that both estrogen alone and estrogen plus progestin increase the risk of developing breast cancer.
The researchers explain that:
“An imbalance in the use of mammography with greater screening for hormone users could explain some of the increase in breast cancer incidence with estrogen alone seen in cohort studies because screened populations have more cancers detected than unscreened populations.”
Even though the authors do not fully understand the mechanisms underlying the different effects of estrogen alone and estrogen in addition to progestin, they said:
“The findings in the clinic, taken together with preclinical evidence, indicate that many breast cancers in post-menopausal women can survive only a limited range of estrogen exposures.”
Written by Grace Rattue