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Table 2 Risk of breast cancer subgroups defined by clinico-pathological markers in relation to total duration of breastfeeding

From: Breastfeeding in relation to risk of different breast cancer characteristics

Tumour subgroup Breastfeeding total in months Number of cases Incidence/100000 RR RR*
Invasive      
breast cancer** <4.0 80 270 1.00 1.00
  ≥4.0 - <8.0 108 288 1.07 (0.80 - 1.42) 1.04 (0.77 - 1.40)
  ≥8.0 - <13.0 109 304 1.12 (0.84 - 1.49) 1.09 (0.80 - 1.48)
  ≥13.0 103 293 1.08 (0.81 - 1.45) 1.10 (0.78 - 1.54)
  Missing 24 399 --- ---
  Total 424 294 p-trend: 0.56 p-trend:0.45
CIS      
  <4.0 9 30 1.00 1.00
  ≥4.0 - <8.0 19 51 1.67 (0.76 - 3.70) 1.90 (0.84 - 4.30)
  ≥8.0 - <13.0 13 36 1.20 (0.51 - 2.81) 1.40 (0.57 - 3.46)
  ≥13.0 13 37 1.22 (0.52 - 2.86) 1.59 (0.60 - 4.21)
  Missing 3 50 --- ---
  Total 57 40 p-trend:0.98 p-trend:0.48
Size ≤20 mm#      
  <4.0 55 186 1. 00 1.00
  ≥4.0 - <8.0 80 214 1.15 (0.82 - 1.62) 1.12 (0.79 - 1.60)
  ≥8.0 - <13.0 69 192 1.03 (0.72 - 1.47) 0.99 (0.68 - 1.45)
  ≥13.0 85 241 1.30 (0.93 - 1.82) 1.29 (0.87 - 1.92)
  Missing 15 249 --- ---
  Total 304 211 p-trend:0.21 p-trend:0.24
Size >20 mm      
  <4.0 25 84 1.00 1.00
  ≥4.0 - <8.0 27 72 0.85 (0.50 - 1.47) 0.84 (0.48 - 1.47)
  ≥8.0 - <13.0 39 109 1.28 (0.78 - 2.12) 1.28 (0.75 - 2.20)
  ≥13.0 18 51 0.61 (0.33 - 1.11) 0.65 (0.33 - 1.27)
  Missing 9 150 --- ---
  Total 118 82 p-trend:0.36 p-trend:0.63
Axillary lymph      
node neg# <4.0 27 91 1.00 1.00
  ≥4.0 - <8.0 32 85 0.94 (0.56 - 1.56) 0.91 (0.54 - 1.54)
  ≥8.0 - <13.0 34 95 1.04 (0.63 - 1.72) 0.99 (0.56 - 1.70)
  ≥13.0 31 88 0.97 (0.58 - 1.62) 0.90 (0.50 - 1.64)
  Missing 5 83 --- ---
  Total 129 89 p-trend:0.99 p-trend:0.82
Axillary lymph      
node pos <4.0 53 179 1.00 1.00
  ≥4.0 - <8.0 72 192 1.07 (0.75 - 1.53) 1.05 (0.73 - 1.51)
  ≥8.0 - <13.0 71 198 1.10 (0.77 - 1.57) 1.08 (0.73 - 1.57)
  ≥13.0 71 202 1.13 (0.79 - 1.61) 1.18 (0.78 - 1.79)
  Missing 19 316 --- ---
  Total 286 198 p-trend: 0.52 p-trend:0.30
Grade I#      
  <4.0 27 91 1.00 1.00
  ≥4.0 - <8.0 37 99 1.08 (0.66 - 1.78) 1.01 (0.61 - 1.69)
  ≥8.0 - <13.0 28 78 0.85 (0.50 - 1.45) 0.78 (0.44 - 1.38)
  ≥13.0 28 80 0.87 (0.51 - 1.48) 0.87 (0.47 - 1.61)
  Missing 7 116 --- ---
  Total 127 88 p-trend:0.42 p-trend:0.71
Grade II      
  <4.0 33 111 1.00 1.00
  ≥4.0 - <8.0 47 125 1.12 (0.72 - 1.75) 1.05 (0.67 - 1.66)
  ≥8.0 - <13.0 53 148 1.32 (0.85 - 2.03) 1.15 (0.73 - 1.83)
  ≥13.0 46 131 1.17 (0.75 - 1.83) 0.99 (0.60 - 1.64)
  Missing 12 199 --- ---
  Total 191 132 p-trend:0.40 p-trend:0.97
Grade III##      
  <4.0 20 67 1.00 1.00
  ≥4.0 - <8.0 23 61 0.91 (0.45 - 1.66) 1.00 (0.54 - 1.85)
  ≥8.0 - <13.0 28 78 1.15 (0.65 - 2.05) 1.43 (0.77 - 2.66)
  ≥13.0 29 82 1.22 (0.69 - 2.16) 1.74 (0.89 - 3.41)
  Missing 5 83 --- ---
  Total 105 73 p-trend:0.34 p-trend:0.051
  1. *Adjusted for age at baseline (continuous), education, socioeconomic status, marital status, age at menarche, age at first birth, parity, oophorectomy, age at menopause, oral contraceptive use, hormone replacement therapy use, bmi, alcohol consumption, smoking and height.
  2. **All cases with unilateral invasive breast cancer with tissue samples available for examination.
  3. #Reference group in heterogeneity analyses. ##Heterogeneity: p = 0.031.