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

Breast Cancer Research

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

	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

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

ISSN: 1465-542X