DEPOT MEDROXYPROGESTERONE ACETATE AND BREAST-CANCER - A POOLED ANALYSIS OF THE WORLD-HEALTH-ORGANIZATION AND NEW-ZEALAND STUDIES

Background.-Although depot medroxyprogesterone acetate (DMPA) (Depo-Pr overa) has now been approved for marketing as a contraceptive in the U nited States, there are still unresolved issues about the relation bet ween DMPA and risk of breast cancer. The two substantial case-control studies of this association yielded similar but inconclusive results. Because their designs were compatible, these studies were pooled to ob tain more adequate data for analysis. Design.-Pooled results from two case-control studies. Setting.-New Zealand (entire country), Thailand (three centers), Mexico (one center), and Kenya (one center). Particip ants.-A total of 1768 women with breast cancer and 13905 controls, mos t of whom were younger than 55 years. Main Outcome Measure.-Relative r isk (RR) of breast cancer in women who had used DMPA. Results.-The RR of breast cancer for women who had ever used DMPA was 1.1 (95% confide nce interval [CI], 0.97 to 1.4). There was no increase in risk with in creasing duration of use of DMPA, but RR estimates were higher in cert ain subgroups of women. Further analyses suggested that recent (or cur rent) use was the key factor, with women who had started using DMPA wi thin the previous 5 years estimated to have an RR of 2.0 (95% CI, 1.5 to 2.8). Conclusions.-The increased risk of breast cancer observed in recent (or current) users could be due to enhanced detection of breast tumors in women using DMPA or to acceleration of the growth of preexi sting tumors. Women who had used DMPA more than 5 years previously had no increase in risk of breast cancer, regardless of their duration of use.