Table 3 Joint associationsa of smoking and age at menarche with postmenopausal breast cancer risk

From: Cigarette smoking and postmenopausal breast cancer risk in a prospective cohort

 

Age at menarche (years)

 

⩽12

13–14

⩾15

Smoking status

Never

 HR (95% CI)b

1.00 (reference)

0.98 (0.91–1.06)

0.77 (0.66–0.89)

 Cases

1665

1374

251

 Person-years

401 836

344 288

78 524

Former

 HR (95% CI)b

1.07 (0.99–1.15)

1.00 (0.92–1.08)

1.04 (0.91–1.20)

 Cases

1456

1198

255

 Person-years

326 005

280 890

60 495

Current

 HR (95% CI)b

1.14 (1.03–1.27)

1.15 (1.03–1.28)

1.21 (0.99–1.47)

 Cases

620

515

131

 Person-years

142 563

118 010

29 113

  1. Abbreviations: CI=confidence interval; HR=hazard ratio.
  2. aP-interaction=0.03.
  3. bAdjusted for age at study entry, education level, race/ethnicity, nulliparity/age at first birth, age at and type of menopause, menopausal hormone therapy use, grams of alcohol consumed per day, BMI, frequency of vigorous physical activity, previous breast biopsy, and family history of breast cancer.
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