Breast Cancer Risk After Radiation Therapy for Hodgkin Lymphoma: Influence of Gonadal Hormone Exposure

BACKGROUND: Young women treated with chest radiation therapy (RT) for Hodgkin lymphoma (HL) experience a strongly increased risk of breast cancer (BC). It is unknown whether endogenous and exogenous gonadal hormones affect RT-associated BC risk. METHODS: We conducted a nested case-control study among female 5-year HL survivors treated before age 41. Hormone exposure and HL treatment data were collected through medical records and questionnaires for 174 BC case patients and 466 control patients. Radiation dose to breast tumor location was estimated based on RT charts, simulation films, and mammography reports. RESULTS: We observed a linear radiation dose-response curve with an adjusted excess odds ratio (EOR) of 6.1%/Gy (95% confidence interval [CI]: 2.1%-15.4%). Women with menopause <30 years (caused by high-dose procarbazine or pelvic RT) had a lower BC risk (OR, 0.13; 95% CI, 0.03-0.51) than did women with menopause ≥50 years. BC risk increased by 6.4% per additional year of post-RT intact ovarian function (P<.001). Among women with early menopause (