Effects of estrogen alone vs. estrogen plus progestin on breast cancer risk

In the past decade, results from large prospective cohort studies and the Women's Health Initiative (WHI) randomized placebo-controlled hormone therapy trials have substantially changed thoughts about how estrogen alone and estrogen plus progestin influence the risk of breast cancer, according to a review published TK in the Journal of The National Cancer Institute.

Although hormone therapy is currently used by millions of women for menopausal symptoms, there is still concern about hormone therapy–induced breast cancer risk. In addition, the effects of estrogen plus progestin versus estrogen alone on breast cancer are not completely understood.

To compare the effects of estrogen alone versus those of estrogen plus progestin on breast cancer risk, 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, looked at data from two randomized, placebo-controlled full scale clinical trials conducted in the WHI. One trial evaluated estrogen plus progestin in postmenopausal women with an intact uterus, and the other evaluated estrogen alone in postmenopausal women with prior hysterectomy. Estrogen plus progestin statistically significantly increased the risk of breast cancer. In contrast, estrogen alone use in postmenopausal women with a previous hysterectomy, statistically significantly decreased the risk of breast cancer.

The randomized clinical trial findings differ from the predominance of observational studies, which suggested that both estrogen alone and estrogen plus progestin increase breast cancer incidence. Dr. Chlebowksi explains 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."

Breast cancer is the second most common cancer in women world-wide with 1.05 million new cases being estimated in the year 2001. In developed countries, it is the most common cancer in women. Populations from countries of North America are at high risk of breast cancer, with incidence rates in US white women going up to 103.7 per 100,000. High rates are also reported from Europe and Australia. In the United Kingdom, nearly 30,000 new cases of breast cancer are diagnosed every year with nearly 15,000 deaths reported from this disease.

The incidence rate of breast cancer has been rising both in the developed and developing countries and it is becoming frequent in some developing countries like Egypt and Tunisia. Carcinoma breast is the second most common cancer among Indian women, and an increasing trend in its incidence has been observed in most of the metropolis with Mumbai toping the list.

Sex-hormones have been implicated in various human cancers such as endometrial cancer, breast and prostatic cancer (among sex-organ related neoplasm) or colon cancer, gall-bladder cancer, kidney cancer, etc. ( non sex-organ related neoplasm).