Effects of Irradiation for Cervical Cancer on Subsequent Breast Cancer.

Abstract

Previous research suggests that cervical cancer patients have a lower risk of breast cancer than women in the general population. Possible explanations include opposing risk factors for cervical cancer and breast cancer, the effect of irradiation used to treat cervical cancer, or both. The purpose of this study was to explore the relationship between irradiation for cervical cancer and the subsequent development of breast cancer. Other factors which influence the development of breast cancer in cervical cancer patients were also investigated. Data from a matched case-control study conducted at four U.S. cancer registries were used. All women had primary cervical cancer. Cases developed breast cancer 5 or more years after cervical cancer; whereas, controls remained free of second primary cancers. There were 118 cases and 953 controls. There was no statistically significant relationship between radiation to the ovarian area and the risk of breast cancer in this study. However, the results were consistent with a 19% reduction in risk for women irradiated for cervical cancer when compared to nonirradiated women. In a dose-response analysis, there was a nonsignificant trend of decreased risk of breast cancer with increased radiation up to 1800 rad. There was no consistent pattern for higher doses. The trend, although nonsignificant, differed by age. Women <60 years of age at irradiation were generally at a lower risk of breast cancer than nonirradiated women. Women over 59 years were at an increased risk. Radiation of (GREATERTHEQ)8 rad to the breast was positively, although nonsignificantly, associated with breast cancer in women who ovaries had been removed. In a comparison of known risk factors, cases were more frequently nulliparious, had fewer children, were taller, and had a positive family history of breast cancer. However, missing data and data more frequently available for cases than controls suggest cautious interpretation. There are some potentially important findings from this study which might influence medical care. These should be examined in the larger International Radiation Study.