Table 4.

Relationship between age at menarche, breast feeding history, and risk of breast cancer subtypesa

Luminal ALuminal BTriple-negativeHER2-overexpressing
n (%)n (%)OR (95% CI)n (%)OR (95% CI)n (%)OR (95% CI)
Age at menarche
 <12105 (19.8)17 (21.5)1.00 (ref)169 (22.1)1.00 (ref)64 (21.6)1.00 (ref)
 12–13308 (58.0)49 (62.0)0.95 (0.52–1.73)439 (57.4)0.90 (0.67–1.19)167 (56.4)0.88 (0.61–1.26)
 ≥14118 (22.2)13 (16.5)0.64 (0.30–1.39)157 (20.5)0.83 (0.59–1.16)65 (22.0)0.88 (0.57–1.36)
 Every 2-year0.89 (0.65–1.22)0.92 (0.79–1.06)0.98 (0.81–1.18)
Ptrend0. 4740.2460.828
Ever breast fed a childb
 No85 (21.3)8 (14.0)1.00 (ref)144 (25.0)1.00 (ref)58 (23.7)1.00 (ref)
 Yes314 (78.7)49 (86.0)1.30 (0.57–2.94)432 (75.0)0.77 (0.56–1.06)187 (76.3)0.80 (0.54–1.19)
Breast feeding duration (in months)b
 Never85 (21.3)8 (14.0)1.00 (ref)144 (25.0)1.00 (ref)58 (23.7)1.00 (ref)
 < 6124 (31.1)13 (22.8)0.90 (0.35–2.33)165 (28.6)0.75 (0.52–1.07)63 (25.7)0.69 (0.44–1.10)
 6–1171 (17.8)9 (15.8)1.08 (0.38–3.01)105 (18.2)0.83 (0.55–1.25)50 (20.4)0.95 (0.57–1.57)
 12–2364 (16.0)11 (19.3)1.37 (0.50–3.72)94 (16.3)0.82 (0.53–1.26)34 (13.9)0.71 (0.41–1.22)
 24–3532 (8.0)7 (12.3)1.79 (0.58–5.53)47 (8.2)0.82 (0.48–1.40)20 (8.2)0.83 (0.43–1.62)
 36+23 (5.8)9 (15.8)3.47 (1.17–10.33)c21 (3.6)0.51 (0.27–0.99)c20 (8.2)1.18 (0.59–2.37)
 Every 6 months1.13 (1.03–1.23)c0.96 (0.91–1.02)1.01 (0.95–1.08)
Ptrend0.0080.1510.716
  • aAnalyses were restricted to Seattle cases who completed the interview. ORs were adjusted for age at diagnosis and year of diagnosis.

  • bRestricted to parous women.

  • cStatistically significant at P < 0.05.