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Table 3 Association between parity (ever versus never) and HER2+ BC at specific ages (age 35, 55 and 75 years)

From: Reproductive profiles and risk of breast cancer subtypes: a multi-center case-only study

  Age at BC diagnosis Odds ratio (95% CI) P value P value interaction parity × age
Luminal A-like At 35 years 1.00 (Ref.)   
At 55 years 1.00 (Ref.)   
At 75 years 1.00 (Ref.)   
HER2+ BC At 35 years 1.44 (1.02–2.03) 0.037  
At 55 years 1.42 (1.04–1.96) 0.029  
At 75 years 0.67 (0.67–0.98) 0.041 0.003
  1. We combined luminal human epidermal growth factor receptor-2 (HER2)-like and HER2-like breast cancer (BC), and investigated whether parity may be associated with the risk of developing HER2+ BC. Interactions between parity and age at BC diagnosis on the probability to develop a specific BC subtype were tested by logistic regression models with binary outcome (1 for HER2+ BC and 0 for luminal A-like BC as the reference subtype) considering parity and age at diagnosis (as a continuous variable) as explanatory variables. A random intercept was introduced to account for clustering by study. The interaction between age and parity on HER2+ BC risk was tested, across all ages and, because age was modeled non-linearly, also specifically at age 35, 55 and 75 years