title: Hormone therapy and young-onset breast cancer.
abstract: Estrogen plus progestin hormone therapy (HT) is associated with an increased risk of postmenopausal breast cancer, but few studies have examined the impact of HT use on the risk of breast cancer in younger women. We assessed the association between estrogen plus progestin HT or unopposed estrogen HT and young-onset breast cancer using data from the Two Sister Study (2008-2010), a sister-matched study of 1,419 cases diagnosed with breast cancer before the age of 50 years and 1,665 controls. We assessed exposures up to a family-specific index age to ensure comparable opportunities for exposures and used propensity scores to control for birth cohort effects on HT use. Ever HT use was uncommon (7% and 11% in cases and controls, respectively). Use of estrogen plus progestin was not associated with an increased risk of young-onset breast cancer (odds ratio = 0.80, 95% confidence interval: 0.41, 1.59). Unopposed estrogen use was inversely associated with the risk of young-onset breast cancer (odds ratio = 0.58, 95% confidence interval: 0.34, 0.99). Duration of use, age at first use, and recency of use did not modify these associations.
authors.forename: Katie M
authors.initials: KM
authors.lastname: O'Brien
authors.forename: Chunyuan
authors.initials: C
authors.lastname: Fei
authors.forename: Dale P
authors.initials: DP
authors.lastname: Sandler
authors.forename: Hazel B
authors.initials: HB
authors.lastname: Nichols
authors.forename: Lisa A
authors.initials: LA
authors.lastname: DeRoo
authors.forename: Clarice R
authors.initials: CR
authors.lastname: Weinberg
mesh_terms: D000328:Adult; D017668:Age of Onset; D000368:Aged; D001943:Breast Neoplasms / Q000209:etiology* / Q000235:genetics; D016022:Case-Control Studies; D015914:Estrogen Replacement Therapy / Q000009:adverse effects*; D004967:Estrogens / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008875:Middle Aged; D017697:Premenopause; D011372:Progestins / Q000009:adverse effects*; D057216:Propensity Score; D012307:Risk Factors; D035781:Siblings
chemical_list: D004967:Estrogens; D011372:Progestins
keywords: hormone therapy; propensity score; young-onset breast cancer