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Table 3 Case-control ORs of breast cancer risk factors by age among premenopausal women in Carolina Breast Cancer Study phases I and II (n = 1904)

From: Breast cancer biologic and etiologic heterogeneity by young age and menopausal status in the Carolina Breast Cancer Study: a case-control study

  Age <40 years Age ≥40 years Test for heterogeneity
Risk factor Control subjects, n (%) Cases, n (%) OR (95 % CI)a Control subjects, n (%) Cases, n (%) OR (95 % CI)a χ2 test, df (p value)b
BMI, kg/m2
 < 25.0 93 (41.9) 154 (49.2) 1.0 255 (40.0) 316 (44.3) 1.0 0.13, 2 (0.9)
 25–29.9 58 (26.1) 71 (22.7) 0.72 (0.45–1.13) 184 (28.9) 181 (25.4) 0.87 (0.65–1.14)  
 ≥ 30.0 71 (32.0) 88 (28.1) 0.73 (0.47–1.13) 198 (31.1) 217 (30.4) 0.98 (0.74–1.29)  
 Missing     12 6   
WHR
 < 0.77 89 (41.4) 135 (44.3) 1.0 235 (36.8) 231 (32.4) 1.0 2.47, 2 (0.3)
 0.77–0.83 68 (31.6) 98 (32.1) 0.94 (0.61–1.43) 209 (32.7) 245 (34.4) 1.42 (1.08–1.86)  
 ≥ 0.84 58 (27.0) 72 (23.6) 0.86 (0.54–1.36) 195 (30.5) 237 (33.2) 1.58 (1.18–2.11)  
 Missing 7 8   10 7   
Parity
 Nulliparous 49 (22.1) 70 (22.4) 1.0 76 (11.7) 106 (14.7) 1.0 3.55, 2 (0.2)
 1–2 births 133 (59.9) 180 (57.5) 1.05 (0.67–1.63) 383 (59.0) 420 (58.3) 0.82 (0.58–1.14)  
 ≥ 3 births 40 (18.0) 63 (20.1) 1.29 (0.74–2.27) 190 (29.3) 194 (26.9) 0.81 (0.55–1.18)  
History of breastfeedingc
 Never 77 (44.5) 145 (60.2) 1.0 343 (60.2) 370 (60.6) 1.0 9.01, 1 (0.003)
 Ever 96 (55.5) 96 (39.8) 0.48 (0.31–0.75) 227 (39.8) 241 (39.4) 0.90 (0.70–1.16)  
Lifetime breastfeeding durationc
 Never 86 (49.7) 148 (61.4) 1.0 346 (60.7) 378 (61.9) 1.0 6.36, 2 (0.04)
 > 0–3 months 25 (14.5) 33 (13.7) 0.79 (0.43–1.45) 69 (12.1) 65 (10.6) 0.86 (0.58–1.25)  
 ≥ 4 months 62 (35.8) 60 (24.9) 0.50 (0.30–0.81) 155 (27.2) 168 (27.5) 0.87 (0.65–1.15)  
Time since last term pregnancyc
 < 10 years 119 (68.8) 169 (70.1) 1.0 76 (13.3) 108 (17.7) 1.0 4.44, 2 (0.1)
 10–19 years 50 (28.9) 66 (27.4) 1.02 (0.64–1.63) 302 (53.0) 283 (46.3) 0.71 (0.50–1.01)  
 ≥ 20 years 4 (2.3) 6 (2.5) 1.14 (0.30–4.27) 192 (33.7) 220 (36.0) 0.96 (0.64–1.43)  
Age at first live birthc
 < 26 years 103 (59.5) 146 (60.6) 1.0 386 (67.7) 414 (67.8) 1.0 0.00, 1 (1.0)
 ≥ 26 years 70 (40.5) 95 (39.4) 1.03 (0.68–1.58) 184 (32.3) 197 (32.2) 0.93 (0.71–1.20)  
Age at last live birthc
 < 30 years 102 (59.0) 148 (61.4) 1.0 344 (60.4) 362 (59.2) 1.0 0.01, 1 (0.9)
 ≥ 30 years 71 (41.0) 93 (38.6) 1.01 (0.67–1.54) 226 (35.6) 249 (40.8) 0.99 (0.78–1.26)  
Age at menarche
 < 13 years 111 (50.2) 170 (54.3) 1.0 323 (49.8) 393 (54.6) 1.0 0.01, 1 (0.9)
 ≥ 13 years 110 (49.8) 143 (45.7) 0.85 (0.59–1.20) 326 (50.2) 327 (45.4) 0.83 (0.66–1.03)  
 Missing 1       
Oral contraceptive use
 Never 33 (14.9) 36 (11.5) 1.0 112 (17.3) 125 (17.4) 1.0 0.67, 1 (0.4)
 Ever 189 (85.1) 276 (88.5) 1.32 (0.78–2.22) 534 (82.7) 593 (82.6) 0.93 (0.70–1.25)  
 Missing   1   3 2   
  1. BMI body mass index, WHR waist-to-hip ratio
  2. aAdjusted for matching factors race and age
  3. bLikelihood ratio tests were performed to assess age-related heterogeneity in risk factor associations by comparing the estimated log-likelihood of adjusted models with that of the adjusted model including a multiplicative interaction term for age and the corresponding risk factor (e.g., BMI × age). Statistically significant heterogeneity by age was defined with α = 0.1
  4. cAmong parous women