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Injectable depot medroxyprogesterone acetate has been used for contraception by millions of women, but it has not been approved in the U.S. because studies found it caused malignant mammary tumors in beagles. Whether such findings are relevant to women is uncertain. This large case-control study in New Zealand, where the drug has been widely used since 1969, compared the contraceptive histories of 891 women with newly diagnosed breast cancer and 1864 controls selected randomly from voter lists.
A similar proportion of patients and controls had used medroxyprogesterone (12.3 percent and 13.5 percent, respectively). Although medroxyprogesterone use overall did not increase the risk of breast cancer, it was associated with elevated risk in cert…