Breast neoplasms in women treated with x-rays for acute postpartum mastitis.

Breast cancer has been studied by mail survey up to 34 years in 571 of 606 women treated with x-rays for acute postpartum mastitis. The incidence of neoplasms was compared with that of three nonirradiated control groups--nonirradiated sisters of the treated women, women with acute postpartum mastitis not treated with X-rays, and their nonirradiated sisters. For the irradiated group, with mean dose of 247 rads to both breasts, the overall relative risk of breast cancer was 2.2 for years 10-34 post irradiation and 3.6 for years 20-34. The dose response for malignant and benign breast neoplasms was compatible with a linear fit. For comparable total doses, fractionation of exposure did not reduce carcinogenic action. Women over age 30 years at radiation treatment had as great an excess risk of breast cancer as did younger women. The overall excess risk of developing breast cancer was about 8-10 cases per million women per rad per year, an increase of about 0.5% per rad.