title: Late age at first full term birth is strongly associated with lobular breast cancer.
abstract: BACKGROUND
  Late age at first full-term birth and nulliparity are known to increase breast cancer risk. The frequency of these risk factors has increased in recent decades.
  
  
  METHODS
  The purpose of this population-based case-control study was to examine associations between parity, age at first birth (AFB), and specific histological subtypes of breast cancer. Women with breast cancer were identified from cancer registries in Wisconsin, Massachusetts, and New Hampshire. Control subjects were randomly selected from population lists. Interviews collected information on reproductive histories and other risk factors. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) of ductal, lobular, and mixed ductal-lobular breast cancer diagnosis in association with AFB and nulliparity.
  
  
  RESULTS
  AFB ≥30 years was associated with a 2.4-fold increase in risk of lobular breast cancer compared with AFB <20 years (OR, 2.4; 95% CI, 1.9-2.9). The association was less pronounced for ductal breast cancer (OR, 1.3; 95% CI, 1.2-1.4). Nulliparity was associated with increased risk for all breast cancer subtypes, compared with women with AFB <20 years, but the association was stronger for lobular (OR, 1.7; 95% CI, 1.3-2.2) than for ductal (OR, 1.2; 95% CI, 1.1-1.3) subtypes (P = .004). The adverse effects of later AFB was stronger with obesity (P = .03) in lobular, but not ductal, breast cancer.
  
  
  CONCLUSIONS
  Stronger associations observed for late AFB and nulliparity suggest that these factors preferentially stimulate growth of lobular breast carcinomas. Recent temporal changes in reproductive patterns and rates of obesity may impact the histological presentation of breast cancer.
authors.affiliation: University of Wisconsin Carbone Comprehensive Cancer Center, Madison, Wisconsin, USA. pnewcomb@fhcrc.org
authors.forename: Polly A
authors.initials: PA
authors.lastname: Newcomb
authors.forename: Amy
authors.initials: A
authors.lastname: Trentham-Dietz
authors.forename: John M
authors.initials: JM
authors.lastname: Hampton
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Egan
authors.forename: Linda
authors.initials: L
authors.lastname: Titus-Ernstoff
authors.forename: Shaneda
authors.initials: S
authors.lastname: Warren Andersen
authors.forename: E Robert
authors.initials: ER
authors.lastname: Greenberg
authors.forename: Walter C
authors.initials: WC
authors.lastname: Willett
mesh_terms: D000328:Adult; D000368:Aged; D001722:Birth Order; D001943:Breast Neoplasms / Q000453:epidemiology*; D044584:Carcinoma, Ductal / Q000453:epidemiology; D018275:Carcinoma, Lobular / Q000453:epidemiology* / Q000473:pathology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D012307:Risk Factors; D047929:Term Birth