I need help in correcting a medical impression that has been considered fact for thirty or forty years. The impression is that therapeutic hormones accelerate breast cancer growth. I believe I know why this false impression is so widespread. A doctor may examine a patient's breasts and order a mammogram which reveals normal findings. Then, two or three months later another examination reveals extensive breast carcinoma and the conclusion is that the hormone caused the rapid growth of the cancer. The hormone was responsible, but not for stimulating the rapid growth. Rather, the hormone was responsible for a "MASKING EFFECT" that gives the impression of rapid growth. The following actual cases illustrates this point.