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Table 4 Associations between breast cancer risk factors and tumor molecular subtypes in Kenyan breast cancer patients (N=821*)

From: Breast cancer risk factors in relation to molecular subtypes in breast cancer patients from Kenya

    Tumor subtypes  
  Luminal A n=286 Luminal B n=294 Luminal B vs. Luminal A HER2-enriched n=88 HER2-enriched vs. Luminal A Triple negative n=153 Triple negative vs. Luminal A
  N % N % OR (95% CI)† P† N % OR (95% CI)† P† N % OR (95% CI)† P†
Age at diagnosis/year
 < 50 142 50.2 180 61.4 1.00 (Ref)   44 50.0 1.00 (Ref)   77 50.3 1.00 (Ref)  
 ≥ 50 141 49.8 113 38.6 0.87 (0.36, 2.06) 0.74 44 50.0 1.84 (0.57, 5.92) 0.30 76 49.7 0.52 (0.20, 1.40) 0.20
BMI/ kg/m2
 Normal (< 25.0) 60 27.3 71 30.5 1.00 (Ref)   29 41.4 1.00 (Ref)   43 32.6 1.00 (Ref)  
 Overweight (25.0–29.9) 84 38.2 99 42.5 1.09 (0.66, 1.82) 0.73 25 35.7 0.55 (0.28, 1.11) 0.10 49 37.1 0.91 (0.49, 1.68) 0.75
 Obese (≥ 30.0) 76 34.5 63 27.0 0.76 (0.43, 1.33) 0.33 16 22.9 0.36 (0.16, 0.81) 0.013 40 30.3 0.89 (0.46, 1.72) 0.73
 Trend‡      0.87 (0.66, 1.15) 0.32    0.59 (0.39, 0.88) 0.011    0.94 (0.68, 1.32) 0.73
Premenopausal: BMIa
 Normal (< 25.0) 36 32.4 51 34.7 1.00 (Ref)   16 45.7 1.00 (Ref)   23 38.3 1.00 (Ref)  
 Overweight (25.0–29.9) 43 38.7 59 40.1 0.98 (0.51, 1.88) 0.95 11 31.4 0.52 (0.19, 1.40) 0.20 16 26.7 0.49 (0.20, 1.21) 0.12
 Obese (≥ 30.0) 32 28.8 37 25.2 0.78 (0.37, 1.61) 0.49 8 22.9 0.44 (0.14, 1.35) 0.15 21 35.0 0.84 (0.34, 2.07) 0.71
 Trend‡      0.89 (0.62, 1.27) 0.52    0.65 (0.37, 1.1) 0.13    0.91 (0.57, 1.45) 0.69
Postmenopausal: BMIa
 Normal (< 25.0) 24 22.0 20 23.5 1.00 (Ref)   13 37.1 1.00 (Ref)   20 27.8 1.00 (Ref)  
 Overweight (25.0–29.9) 41 37.6 40 47.1 1.35 (0.57, 3.20) 0.50 14 40.0 0.48 (0.17, 1.40) 0.18 33 45.8 1.70 (0.68, 4.26) 0.25
 Obese (≥ 30.0) 44 40.4 25 29.4 1.10 (0.43, 2.82) 0.84 8 22.9 0.24 (0.07, 0.81) 0.022 19 26.4 1.28 (0.48, 3.46) 0.62
 Trend‡      1.02 (0.64, 1.64) 0.92    0.47 (0.26, 0.88) 0.018    1.10 (0.68, 1.78) 0.71
Age at menarche/year
 ≤ 13 (9–13) 69 25.8 71 24.8 1.00 (Ref)   23 26.4 1.00 (Ref)   33 22.9 1.00 (Ref)  
 14 68 25.4 69 24.1 1.28 (0.73, 2.25) 0.39 26 29.9 1.65 (0.73, 3.74) 0.23 37 25.7 1.43 (0.73, 2.81) 0.30
 ≥ 15 (15–20) 131 48.9 146 51.1 1.29 (0.79, 2.13) 0.31 38 43.7 1.32 (0.64, 2.73) 0.46 74 51.4 1.43 (0.78, 2.60) 0.24
 Trend‡      1.13 (0.88, 1.45) 0.34    1.12 (0.78, 1.59) 0.54    1.18 (0.88, 1.58) 0.28
Age at first pregnancy/year
 < 20 72 26.2 58 19.9 1.00 (Ref)   31 35.6 1.00 (Ref)   51 34.0 1.00 (Ref)  
 20–24 121 44.0 133 45.5 1.51 (0.84, 2.70) 0.17 30 34.5 0.64 (0.29, 1.37) 0.25 69 46.0 0.81 (0.43, 1.51) 0.51
 25–29 51 18.5 62 21.2 1.76 (0.85, 3.65) 0.13 16 18.4 0.92 (0.34, 2.51) 0.87 19 12.7 0.67 (0.28, 1.60) 0.37
 Nulliparousb or ≥ 30 31 11.3 39 13.4 1.06 (0.40, 2.82) 0.90 10 11.5 1.18 (0.31, 4.53) 0.81 11 7.3 0.66 (0.20, 2.18) 0.50
 Trend‡      1.09 (0.82, 1.45) 0.54    1.02 (0.67, 1.56) 0.93    0.84 (0.59, 1.20) 0.33
Parity
 Nulliparousb 14 4.9 20 6.8 1.09 (0.30, 3.88) 0.90 4 4.5 0.56 (0.07, 4.77) 0.60 3 2.0 0.67 (0.11, 4.12) 0.66
 Parous 272 95.1 274 93.2 1.00 (Ref)   84 95.5 1.00 (Ref)   150 98.0 1.00 (Ref)  
Number of children
 1–2 73 26.8 101 36.9 1.00 (Ref)   19 22.6 1.00 (Ref)   31 20.7 1.00 (Ref)  
 3–4 113 41.5 101 36.9 0.47 (0.28, 0.79) 0.005 26 31.0 0.85 (0.37, 1.98) 0.71 59 39.3 1.16 (0.59, 2.29) 0.66
 ≥ 5 86 31.6 72 26.3 0.45 (0.23, 0.87) 0.018 39 46.4 1.71 (0.65, 4.53) 0.28 60 40.0 1.27 (0.56, 2.89) 0.56
 Trend‡      0.65 (0.47, 0.90) 0.0099    1.34 (0.82, 2.20) 0.24    1.11 (0.75, 1.66) 0.60
Cumulative breastfeeding duration/monthc
 Q1: 1–< 39 64 24.3 88 33.2 1.00 (Ref)   15 18.3 1.00 (Ref)   20 13.9 1.00 (Ref)  
 Q2: 39–< 62 59 22.4 68 25.7 0.99 (0.54, 1.80) 0.97 22 26.8 2.48 (0.97, 6.33) 0.058 40 27.8 2.98 (1.33, 6.71) 0.008
 Q3: 62–< 96 71 27.0 53 20.0 0.66 (0.33, 1.30) 0.23 14 17.1 0.80 (0.27, 2.39) 0.69 40 27.8 1.80 (0.74, 4.38) 0.20
 Q4: ≥ 96 69 26.2 56 21.1 0.99 (0.44, 2.20) 0.97 31 37.8 1.30 (0.40, 4.16) 0.66 44 30.6 1.87 (0.69, 5.07) 0.22
 Trend‡      0.93 (0.71, 1.20) 0.56    0.97 (0.67, 1.41) 0.88    1.12 (0.82, 1.52) 0.47
Mean breastfeeding duration per child/month
 < 12 34 12.9 48 18.1 1.00 (Ref)   11 13.4 1.00 (Ref)   23 16.0 1.00 (Ref)  
 12– 23 142 54.0 139 52.5 0.65 (0.35, 1.21) 0.18 49 59.8 1.24 (0.47, 3.29) 0.66 71 49.3 0.75 (0.36, 1.59) 0.46
 ≥ 24 87 33.1 78 29.4 0.64 (0.32, 1.27) 0.20 22 26.8 1.21 (0.42, 3.52) 0.73 50 34.7 1.09 (0.49, 2.43) 0.83
 Trend‡      0.84 (0.60, 1.16) 0.28    1.07 (0.66, 1.72) 0.80    1.13 (0.76, 1.66) 0.55
Age at first pregnancy and Number of children
 Age 25+ years, 1–3 births 54 20.7 64 23.5 1.00 (Ref)   15 17.9 1.00 (Ref)   20 13.6 1.00 (Ref)  
 Age < 25 years, 1–3 births 80 30.7 93 34.2 0.93 (0.52, 1.67) 0.81 19 22.6 0.82 (0.31, 2.15) 0.69 47 32.0 1.39 (0.65, 2.97) 0.40
 Age 25+ years, 4+ births 15 5.7 18 6.6 0.77 (0.29, 2.05) 0.60 8 9.5 2.10 (0.58, 7.54) 0.26 7 4.8 1.12 (0.29, 4.27) 0.87
 Age < 25 years, 4+ births 112 42.9 97 35.7 0.55 (0.29, 1.05) 0.068 42 50.0 1.31 (0.51, 3.39) 0.58 73 49.7 1.38 (0.62, 3.08) 0.43
 Trend‡      0.81 (0.66, 0.99) 0.041    1.16 (0.86, 1.56) 0.33    1.07 (0.84, 1.37) 0.58
Number of children and Cumulative breastfeeding duration
 Nulliparous or ≤ 3 children and < 62 months 117 42.2 146 51.2 1.00 (Ref)   31 36.0 1.00 (Ref)   51 34.7 1.00 (Ref)  
 ≤ 3 children and ≥ 62 months 30 10.8 25 8.8 0.61 (0.30, 1.22) 0.16 6 7.0 0.41 (0.11, 1.56) 0.19 17 11.6 1.19 (0.53, 2.66) 0.68
 ≥ 4 children and < 62 months 20 7.2 30 10.5 0.89 (0.38, 2.07) 0.79 10 11.6 2.34 (0.78, 6.99) 0.13 12 8.2 1.31 (0.49, 3.53) 0.59
 ≥ 4 children and ≥ 62 months 110 39.7 84 29.5 0.52 (0.30, 0.89) 0.02 39 45.3 1.26 (0.57, 2.78) 0.56 67 45.6 0.96 (0.50, 1.84) 0.91
 Trend‡      0.81 (0.68, 0.97) 0.02    1.11 (0.85, 1.44) 0.44    0.99 (0.80, 1.22) 0.91
Menopausal statusa
 Premenopausal 144 50.3 174 59.4 1.00 (Ref)   44 50.0 1.00 (Ref)   68 44.7 1.00 (Ref)  
 Postmenopausal 142 49.7 119 40.6 0.69 (0.32, 1.48) 0.33 44 50.0 0.69 (0.22, 2.10) 0.51 84 55.3 1.82 (0.78, 4.28) 0.17
Age at menopause/year
 Premenopausal 144 50.3 174 59.4 N/A 44 50.0 N/A 68 44.7 N/A
 < 50 years 58 22.5 58 20.9 1.00 (Ref)   28 33.7 1.00 (Ref)   44 32.1 1.00 (Ref)  
> 50 years 56 21.7 46 16.6 0.88 (0.45, 1.74) 0.72 11 13.3 0.38 (0.15, 0.997) 0.049 25 18.3 0.66 (0.31, 1.40) 0.28
  1. *Seventeen cases were excluded from analyses because of their missing data for HER2 status. † Point estimates and 95% confidence intervals were from multivariable models, adjusting for the same series of covariates (except where noticed): age at diagnosis, BMI, age at menarche, age at first pregnancy, number of children, mean breastfeeding duration per child, age at menopause, family history of breast cancer in first-degree female relative, occupation, education level, and location of the facility. Estimates of numbers of children, cumulative and mean breastfeeding duration, and combined age at first pregnancy, and number of children were computed among parous women. ‡ Results were from the trend analysis using the categorical risk factor as a trend. a Multivariable modeling analysis without adjusting for age at menopause. bWomen who reported never pregnant, never gave birth, and had no child were grouped as "Nulliparous" in modeling analyses. c Multivariable modeling analysis without adjusting for mean breastfeeding duration per child. BMI, body mass index; CI, confidence interval; HER2, human epidermal growth factor receptor-2; OR, odds ratio; Q, quartile