Cigarette smoking at early age and breast cancer in the U.S. radiologic technologist health study

Purpose We examined risk of breast cancer associated with cigarette smoking in the U.S. Radiologic Technologists cohort. In particular, we evaluated age of smoking initiation in pre- versus postmenopausal breast cancer. Methods We followed 56,042 female radiologic technologists (RT) who responded to a baseline questionnaire (1983–1989) and were cancer-free (excluding nonmelanoma skin cancer) through completion of a second questionnaire (1994–1998). A total of 906 invasive breast cancer cases (781 incident primary breast cancers and 125 deaths) were identified through self-reports; 83% were validated through medical records or death certificates. We constructed two cohorts of 43,670 pre- and 24,748 postmenopausal women, within which 318 and 588 incident breast cancer cases occurred, respectively. Using Cox proportional hazard regression models with age as the time-scale, stratified at baseline for birth cohort in 5-year intervals, and adjusted for alcohol drinks per week, age at menarche, age at first live birth, parity, family history of breast cancer, hormone replacement therapy, year first worked as a RT, and body mass index, we evaluated a simultaneous model using four smoking variables: age of cigarette smoking initiation, pack-years of smoking, smoking status (current, quit 3–15 years ago, quit 16 or more years ago), and smoking (ever, never). Results Breast cancer risks increased with decreasing age smoking was initiated (Ptrend = 0.04, postmenopausal cohort). The breast cancer risk for postmenopausal women who began smoking before age 15 was significantly increased (hazard ratio = 1.77, 95% confidence interval = 1.14–2.75) compared with those who began smoking after age 20. Neither smoking status nor ever–never smoking was associated with breast cancer risk when age at smoking initiation was included in the postmenopausal Cox model. Within the premenopausal cohort, age at smoking initiation was not associated with breast cancer risk. Conclusion Postmenopausal women who began smoking at an early age (under 15) had a significantly elevated risk of breast cancer compared with postmenopausal women who began smoking at age 20 or older.