Table 3.

Multivariable analyses for associations of risk factors with invasive breast cancer among women age ≥45 years, by ER statusa

All invasive (n = 1,534)ER (n = 385)ER+ (n = 804)
Person-yearsCasesHR (95% CI)CasesHR (95% CI)CasesHR (95% CI)
Age at menarche (y)
 ≤11124,0564421.00 (reference)1221.00 (reference)2271.00 (reference)
 12–13238,2488180.94 (0.84–1.06)1920.80 (0.63–1.00)4441.00 (0.85–1.18)
 ≥1494,4872700.77 (0.66–0.90)710.72 (0.53–0.97)1310.73 (0.59–0.91)
Oral contraceptive use
 Never113,2143971.00 (reference)721.00 (reference)2201.00 (reference)
 Ever, ≥10 years ago304,71710081.07 (0.95–1.22)2811.54 (1.17–2.03)5180.99 (0.84–1.17)
 Ever, 5–10 years ago17,513561.34 (1.00–1.80)161.95 (1.10–3.46)251.08 (0.70–1.66)
 Ever, within 5 years23,408731.37 (1.05–1.80)161.51 (0.85–2.69)411.38 (0.96–1.98)
Family history of breast cancer
 No411,59112921.00 (reference)3311.00 (reference)6771.00 (reference)
 Yes47,2692421.57 (1.36–1.80)541.39 (1.04–1.86)1271.55 (1.28–1.88)
Parity
 Nulliparous85,0332751.02 (0.84–1.24)510.71 (0.48–1.07)1561.17 (0.90–1.52)
 1 birth105,6853771.00 (reference)911.00 (reference)1981.00 (reference)
 2 births134,0264490.93 (0.81–1.07)1311.09 (0.83–1.43)2280.90 (0.74–1.09)
 3+ births132,0984320.84 (0.71–0.98)1120.92 (0.68–1.26)2210.80 (0.64–0.99)
Age at first birth (years)b
 <20125,4263971.00 (reference)1121.00 (reference)2001.00 (reference)
 20–24128,9294301.00 (0.87–1.15)1201.01 (0.77–1.31)2150.98 (0.80–1.19)
 ≥25111,7474121.14 (0.98–1.33)990.97 (0.72–1.32)2211.20 (0.97–1.49)
Years since last birthb
 ≥10 years350,94811981.00 (reference)3256171.00 (reference)
 <10 years10,107261.09 (0.73–1.65)2141.18 (0.67–2.08)
Lactationb
 Never220,4787461.00 (reference)2021.00 (reference)3731.00 (reference)
 Ever145,8854971.04 (0.93–1.18)1281.01 (0.80–1.27)2661.12 (0.95–1.32)
BMI at age 18 (kg/m2)
 <20202,7907271.00 (reference)1911.00 (reference)3821.00 (reference)
 20–24196,5336400.90 (0.81–1.01)1590.87 (0.70–1.09)3310.88 (0.76–1.03)
 ≥2550,3531350.76 (0.63–0.93)310.73 (0.49–1.09)750.80 (0.61–1.04)
Current BMI (kg/m2)
 <2596,9423371.00 (reference)841.00 (reference)1691.00 (reference)
 25–29.9158,6605270.95 (0.82–1.09)1481.04 (0.79–1.37)2791.00 (0.82–1.21)
 ≥30198,6046591.00 (0.87–1.16)1510.87 (0.65–1.17)3521.08 (0.88–1.32)
Waist:hip ratio
 Tertile 1 (<0.76)105,2043241.00 (reference)811.00 (reference)1671.00 (reference)
 Tertile 2 (0.76–0.84)116,5883831.05 (0.91–1.22)1061.17 (0.87–1.57)2091.11 (0.90–1.36)
 Tertile 3 (>0.84)115,3053801.07 (0.92–1.25)981.11 (0.82–1.51)1951.04 (0.84–1.29)
Alcohol consumption (drinks)
 <1/week317,12110791.00 (reference)2741.00 (reference)5651.00 (reference)
 1–6/week118,3613760.94 (0.83–1.06)900.90 (0.71–1.15)2030.96 (0.82–1.13)
 ≥7/week22,950791.01 (0.80–1.27)211.07 (0.68–1.68)360.88 (0.63–1.24)
Vigorous exercise
 None243,2728581.00 (reference)2231.00 (reference)4501.00 (reference)
 <5 hours/week178,5815620.94 (0.84–1.04)1340.83 (0.67–1.04)2970.95 (0.82–1.10)
 ≥5 hours/week33,3551030.94 (0.76–1.16)260.88 (0.58–1.33)510.92 (0.68–1.23)
  • aMultivariable HRs adjusted for age, smoking history (never active or passive, passive only, never active/unknown passive, 1–<10 packyears, 10+ packyears), menopausal status (premenopausal, hysterectomy only, postmenopausal age <40, postmenopausal age 40–44, postmenopausal age ≥45, postmenopausal age unknown or missing), postmenopausal hormone use (never, E+P <5 years duration, E+P 5+ years duration, other type), and all factors in Table 3.

  • bAmong parous women only. Estimates for age at first birth adjusted for age, smoking history, menopausal status, and all factors in Table 3 except years since last birth; estimates for years since last birth adjusted for age, smoking history, menopausal status, and all factors in Table 3 except age at first birth; estimates for lactation adjusted for age, smoking history, menopausal status, and all factors in Table 3.