Oral contraceptives and reproductive cancers: weighing the risks and benefits.

The hypothetical incidence of reproductive cancers resulting from oral contraceptive use was estimated in several models comparing the cumulative lifetime incidence of cancer of the breast, cervix, ovary and endometrium expected in pill users with the incidence expected in nonusers. The potential number of cancer-free days that would be gained or lost by pill users was compared with similar estimates among nonusers. If five years or more of pill use were associated with a 20% increase in the risk of breast cancer being diagnosed before age 50, a 20% increase in cervical cancer risk and a 50% reduction in the risks of ovarian and endometrial cancers, then every 100,000 pill users would experience 44 fewer reproductive cancers during their lifetime than would nonusers, and would gain one more day free of cancer. If higher estimates of the five-year pill-associated risks of breast and cervical cancer are used--a 50% increased risk of each, for example--then pill users would experience more reproductive cancers than nonusers and would have 11 fewer cancer-free days of life.