Abstract B54: Reproductive status at first diagnosis influences risk of radiation-induced second primary contralateral breast cancer in The WECARE Study

Abstract

Abstract The breast undergoes changes in composition, function and hormonal milieu during puberty, pregnancy, lactation and postmenopausal involution. These changes may influence the susceptibility of the breast to carcinogens, including exposure to ionizing radiation. The Women's Environmental, Cancer and Radiation Epidemiology (WECARE) Study is a multi-center, population-based, case-control study of 708 women (cases) with asynchronous contralateral breast cancer (CBC) and 1,399 women (controls) with unilateral breast cancer (UBC). Radiation therapy (RT) records were used to reconstruct the radiation dose to the location in the contralateral breast where the second cancer arose (or to the equivalent breast location for UBC controls). Rate ratios (RR) and 95% confidence intervals (CI) were computed to assess the relationship between reproductive status at first breast cancer diagnosis, RT and risk of CBC, adjusting for known breast cancer risk factors: age at (first) diagnosis, menopausal status/age at menopause at first diagnosis, age at menarche, number of full-term pregnancies, first degree family history of breast cancer, histology and stage of first primary breast cancer, and treatment (chemotherapy/hormonal therapy). Women who were nulliparous at first diagnosis and exposed to ≥1 gray (Gy) to the contralateral breast, had a higher risk of CBC than unexposed nulliparous women (RR=2.2, 95% CI 1.2–4.0). An increased risk was not seen in RT exposed parous women (RR=1.1, 95% CI 0.8–1.4). Women treated with RT who later became pregnant had a greater risk of CBC compared with unexposed women who also became pregnant (RR=6.0, 95% CI 1.3, 28.4), though these results were based on small numbers. The effect of radiation on risk of CBC did not vary by number of pregnancies, history of breast feeding or menopausal status at the time of first breast cancer diagnosis. These results suggest that RT may be associated with an increased risk of developing a second breast cancer in nulliparous but not parous women. Women who become pregnant after first breast cancer diagnosis may also be at an increased risk of CBC. It is possible that RT could be the initiating event, leading to preneoplastic cellular changes that are then promoted by the hormonal changes of a subsequent pregnancy. Citation Information: Cancer Prev Res 2011;4(10 Suppl):B54.