Mayo Clinic Proc.: Oral Contraceptive Use as a Risk Factor for Premenopausal Breast Cancer: A Meta-Analysis.

• Author: Kahlenborn, Chris
• Position: Reprint

Breast cancer is the leading cause of cancer in women worldwide and the most common cause of cancer death in U.S. women aged 20 to 59 years. Each year in the United States, approximately 211,000 women develop breast cancer and more than 47,000 (20%) do so before the age of fifty years. Approximately two in fifteen American women are expected to develop breast cancer in their lifetimes, and nearly 40,000 women die of the disease annually. During the past four decades, breast cancer rates have risen steadily worldwide and have risen even faster in more developed countries, especially among younger women. For example, from 1973 to 1999 the rate of breast cancer in the United States increased in white women younger than fifty years by 9.8% and by 26.4% in African American women younger than fifty years.

Although the medical research community has long recognized breast cancer risk factors such as a positive family history of breast cancer, early menarche, late menopause, nulliparity, and lack of breastfeeding, concordance is lacking regarding the carcinogenic potential of female hormones. The Women's Health Initiative Clinical Trial reported that prolonged exposure to exogenous estrogens and progestins in hormone therapy increases a woman's risk of developing breast cancer. In addition, the World Health Organization recently classified both postmenopausal hormone replacement and oral contraceptives as group 1 carcinogens.

The association between oral contraceptives and risk of subsequent breast cancer has varied within the medical literature over time. Only one of fifteen studies performed before 1980 showed a positive association. However, more recent studies have noted an increase in risk among oral contraceptive users, especially among women who took them before a first full-term pregnancy. The difference between older and more recent findings may be related to the changing pattern of oral contraceptive use; women who took oral contraceptives from the late 1970s through the 1990s were more likely to use them before their first full term pregnancy and for longer periods than women who used them in the 1960s and early 1970s. Women who are exposed to carcinogens before their first full term pregnancy may have a higher...