Abstract P1-07-05: Weight change across the life-course and breast cancer risk among pre and postmenopausal women
Authors: Colditz G , Eliassen H , Toriola A , Hankinson S , Willett W , Rosner B 
Published: May 2016

Abstract
Obesity is well established as a cause of postmenopausal breast cancer incidence and mortality. In contrast, adiposity in early life is inversely related to breast cancer incidence. To better integrate understanding of these relations, we assess adiposity in childhood, in late adolescence, and in adult years, as well as change in weight in relation to total invasive breast cancer and subtype defined by receptor status.
The Nurses' Health Study cohort was established in 1976 when 121,701 female US registered nurses ages 30-55 responded to a mailed questionnaire about risk factors for breast cancer including reproductive factors, hormone use, anthropometric variables, benign breast disease (BBD), and family history of breast cancer. The risk factors have been updated by repeat questionnaires every 2 years. We followed a cohort of 77,232 women from 1980 to 2006 (1,408,188 person-years), with routinely updated risk factor information, documenting 4,254 incident cases of invasive breast cancer. ER and PR status were obtained from pathology reports and medical records. A total of 2,065 ER+/PR+ tumors, 604 ER-/PR- tumors, 520 ER+/PR- tumors were identified among women with complete information on breast cancer risk factors.
Weight at age 18 was inversely related to incidence of pre and postmenopausal breast cancer. The relative risk (RR) per 50lb weight difference at age 18 was 0.80 (95% CI = 0.73, 0.88). However, the inverse association is completely explained by weight at age 10. Weight at age 10 was more strongly inversely related to ER-PR- breast cancer, RR per 50lb difference in weight at age 10 = 0.48; 95% CI 0.32 – 0.74. Weight gain from 10 to 18 was not related to risk. After controlling for weight at age 18, weight loss of 10lb or more was significantly related to lower risk of breast cancer (RR=0.80; 0.66, 0.95) overall. The association was stronger for premenopausal breast cancer (RR=0.51; 0.30, 0.88). Long-term weight change was positively related to total incident breast cancer risk and most clearly to postmenopausal cancer (RR per 50lb weight gain since age 18 =1.26; 1.19-1.34). Weight gain during premenopausal years (weight at menopause minus weight at age 18), and after menopause, were both directly related to increased risk. Weight gain of 30 or more pounds during premenopause increased risk of postmenopausal breast cancer compared to less than 10lb weight change (RR=1.25; 1.14-1.38) and weight gain of 30 or more pounds after menopause carried similar increase in relative risk (RR=1.24; 1.10-1.41). These results were unchanged after control for weight at age 10, and were stronger for ER+PR+ breast cancer. The associations for long-term weight gain and postmenopausal breast cancer are stronger for never vs. ever users of hormone therapy, but are significantly positively associated in both groups.
In conclusion, adiposity in childhood has a protective lifelong relation to breast cancer risk most clearly seen for ER-PR- disease. There are deleterious effects of long-term weight gain both pre- and post-menopause. Weight loss in premenopausal years significantly reduces risk of breast cancer. Weight change can importantly modify breast cancer risk.
Citation Format: Colditz G, Eliassen H, Toriola A, Hankinson S, Willett W, Rosner B. Weight change across the life-course and breast cancer risk among pre and postmenopausal women. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-07-05.