Table 3.

ORs and 95% CIs for colon and rectal cancer, combined and stratified, according to reproductive factors

CharacteristicControls
Colorectal cancer
Colon cancer
Rectal cancer
n = 4,297* (%)n = 1,488* (%)OR (95% CI)n = 1,122* (%)OR (95% CI)§n = 366* (%)OR (95% CI)
Age at menarche (y)
    <12768 (18.2)238 (19.4)1179 (19.2)159 (19.7)1
    12934 (22.1)326 (23.4)1.03 (0.83-1.29)231 (22.2)1.12 (0.86-1.46)95 (26.8)1.28 (0.90-1.83)
    131,200 (28.4)411 (26.4)1.00 (0.81-1.24)326 (27.2%)1.19 (0.93-1.52)85 (24.0)0.88 (0.62-1.26)
    >141,317 (31.2)468 (30.8)0.99 (0.80-1.22)355 (31.4)1.11 (0.87-1.43)113 (29.5)0.95 (0.67-1.34)
    Ptrend0.90.40.1
Age at first birth (y)
    ≤22.71,896 (50.1)686 (53.8)1537 (55.2)1149 (49.5)1
    >22.7**1,891 (49.9)617 (46.2)0.87 (0.75-1.01)455 (44.8)0.83 (0.70-0.98)162 (50.5)1.08 (0.83-1.41)
    Ptrend††0.40.20.6
Parity
    Nulliparous480 (11.2)165 (12.1)1116 (12.1)149 (12.2)1
    1-21,548 (36.3)464 (33.0)0.94 (0.75-1.18)340 (31.2)0.94 (0.72-1.24)124 (37.8)0.92 (0.64-1.33)
    3-41,543 (36.2)542 (38.3)0.98 (0.78-1.23)415 (29.4)1.02 (0.78-1.34)127 (35.4)0.80 (0.55-1.16)
    >5**697 (16.3)300 (16.7)0.97 (0.76-1.25)240 (17.3)1.10 (0.82-1.48)60 (14.6)0.66 (0.43-1.02)
    Ptrend‡‡1.00.30.05
Menopausal status
    Postmenopausal2,819 (69.8)1,283 (72.2)1975 (72.4)1308 (71.5)1
    Premenopausal1,222 (30.2)157 (27.8)0.67 (0.47-0.97)112 (27.6)0.62 (0.41-0.93)45 (28.5)0.73 (0.38-1.40)
Age at menopause (y)
    <44555 (23.0)238 (22.7)1177 (22.4)161 (23.3)1
    44-50646 (26.8)286 (27.6)1.04 (0.81-1.33)212 (26.7)1.04 (0.78-1.39)74 (30.0)0.98 (0.67-1.45)
    50-52493 (20.4)206 (18.7)0.94 (0.72-1.23)163 (19.5)1.00 (0.74-1.35)43 (16.6)0.72 (0.46-1.12)
    >52717 (29.7)346 (31.1)1.07 (0.85-1.36)266 (31.4)1.18 (0.90-1.54)80 (30.2)0.82 (0.55-1.21)
    Ptrend0.90.60.09
  • * Variable sums that do not equal the total N are due to missing data.

  • Percentages are age-adjusted to the distribution of controls.

  • Conditional on age and study of enrollment; adjusted for family history of colorectal cancer, BMI, education, screening, smoking, hormone replacement therapy, and age at first birth.

  • § Conditional on age and study of enrollment; adjusted for family history of colorectal cancer, BMI, education, screening, smoking, hormone replacement therapy, alcohol consumption, OC use, age at first birth and menopausal status.

  • Conditional on age and study of enrollment; adjusted for family history of colorectal cancer, physical activity, education, screening, smoking, and hormone replacement therapy.

  • Parous women only (Controls: n = 3,787 controls; Colon cancer: n = 992; Rectal cancer: n = 311).

  • ** P < 0.05 for the Wald test comparing colon and rectal associations; all other Wald tests for characteristics in this table have P > 0.05 (unless otherwise indicated).

  • †† P = 0.08 for the Wald test comparing colon and rectal associations.

  • ‡‡ P = 0.06 for the Wald test comparing colon and rectal associations.