Radiotherapy for malignant and benign
gynecologic disease in middle age has been found to be associated inversely with the risk of
breast cancer in several published studies. The ovaries received substantial doses of radiation from such treatments, in the
tens of Gray (Gy) from
radiotherapy for
cervical cancer and one to 10 Gy from
radiotherapy for benign
gynecologic disease (BGD). The relative risk of
breast cancer incidence or mortality decreased with increasing radiation dose to the ovaries between zero to six Gy but varied little with further increases in dose. Evidence of a protective effect even among women irradiated past the age of 50 suggests a mechanism other than that associated with induction of an early menopause. An inverse association with
radiotherapy among women over age 50 was seen only for women with ovarian doses exceeding about four to five Gy, namely, those treated for
cervical cancer or with external beam X-rays for BGD. Ovarian doses of two to three Gy from intrauterine
radium (226Ra) treatments for BGD were not associated with an appreciably reduced risk of
breast cancer, even though the treatments had the intended effect of inducing menopause in women in their mid-40s. The relevant target cells in the ovaries for radiologic menopause likely are those involved in
estrogen production. Although the postmenopausal ovary has largely stopped producing
estrogens, it continues to secrete
androgens. Serum
hormone measurements on a small sample of
cervical cancer patients indicate that high-dose pelvic
radiotherapy eliminates or greatly reduces this residual
androgen-producing activity in ovaries of postmenopausal women.(ABSTRACT TRUNCATED AT 250 WORDS)