title: Body size and the risk of postmenopausal breast cancer subtypes in the California Teachers Study cohort.
abstract: PURPOSE:                       To evaluate how the association between body size and breast cancer risk varies by tumor receptor subtype, host factors, and other exposures among women in the California Teachers Study cohort.                                         METHODS:                       Among 52,642 postmenopausal women, 2,321 developed invasive breast cancer with known estrogen- and progesterone-receptor status (1,652 ER+PR+, 338 ER+PR-, and 312 ER-PR-) between 1995 and 2007. In a subset of 35,529 with waist circumference data, 1,377 developed invasive breast cancer with known ERPR status (991 ER+PR+, 208 ER+PR-, 169 ER-PR-) between 1997 and 2007. Multivariate Cox regression was performed to estimate relative risks (RR) and 95% confidence intervals (CI).                                         RESULTS:                       Obesity, adult weight gain of ≥40 pounds, greater abdominal adiposity, and greater height increased the risk of ER+PR+ breast cancer. The increased risk associated with postmenopausal obesity was limited to those who did not use hormone therapy (HT) at cohort entry (RR = 1.37; 95% CI, 1.05-1.78 for BMI ≥ 30 vs. < 25 kg/m(2); p-interaction = 0.14) and those who were not overweight or obese at age 18 (p-interaction = 0.06). The increased risk associated with greater abdominal adiposity was limited to those who were not also overweight or obese (p-interaction = 0.01). Neither obesity, abdominal adiposity, nor height was associated with the risk of ER-PR- tumors.                                         CONCLUSIONS:                       The effects of body size on postmenopausal breast cancer risk differed by hormone receptor subtype, and among women with ER+PR+ tumors, by HT use and early adult body size.
authors.affiliation: Cancer Prevention Institute of California, 2201 Walnut Avenue, Suite 300, Fremont, CA, 94538, USA, Alison.Canchola@CPIC.org.
authors.forename: Alison J
authors.initials: AJ
authors.lastname: Canchola
authors.forename: Hoda
authors.initials: H
authors.lastname: Anton-Culver
authors.forename: Leslie
authors.initials: L
authors.lastname: Bernstein
authors.forename: Christina A
authors.initials: CA
authors.lastname: Clarke
authors.forename: Katherine
authors.initials: K
authors.lastname: Henderson
authors.forename: Huiyan
authors.initials: H
authors.lastname: Ma
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
authors.forename: Pamela L
authors.initials: PL
authors.lastname: Horn-Ross