PIP: Abortion may increase the risk of breast cancer. Leon Bradlow, M.D., director of the Laboratory of Biochemical Endocrinology and the Strang-Cornell Cancer Research Laboratory in New York, believes that pregnancy protects against breast cancer through the differentiation of breast cells during the second half of pregnancy. Since estrogen, which increases breast cancer risk, is secreted during the first half of pregnancy in order to stimulate breast growth, abortion at that time will expose the mother to high concentrations of estrogen when cells are undifferentiated. Bradlow believes the public should be made aware of studies showing this. Louise Brinton, M.D., of the National Cancer Institute's Division of Cancer Etiology, disagrees because there are many studies that show no link between breast cancer and abortion. Malcolm Pike, M.D., who did the first study linking the two in 1981 (Women less than 33 years of age who had an abortion were 2.4 times more likely to get breast cancer.), declined comment because he had not studied recent data. Holly Howe, Ph.D., of the New York State Department of Health, examined data from fetal death certificates and breast cancer incidence records (1451 women between 1976 and 1980), to find that women (40 years of age) whose pregnancies had been terminated had a relative risk of breast cancer ranging from 1.5 to 1.9. An unpublished study by Janet Daling, M.D., of the Fred Hutchison Cancer Research Center in Seattle, shows a 50% to 90% increase in risk for women who had an abortion before the age of 18. Lynn Rosenberg, M.D., of the Slone Epidemiology Unit of the Boston University School of Medicine, based on a study of 3200 women with breast cancer and 4844 controls, found no relationship between abortion and risk. Brinton is currently conducting a study on breast cancer risk that includes abortion evaluation.