Table 4.

Association between Indigenous American ancestry and demographic variables and reproductive risk factors for breast cancer

% Indigenous American ancestry (n)
P*
ControlsCasesAll
Place of birth
    Foreign born42.6 (200)42.6 (106)42.60.24
    U.S. born40.1 (129)40.8 (128)40.4
Education
    Some high school or less45.3 (169)45.9 (80)45.50.001
    High school graduation40.9 (57)38.0 (49)39.6
    Some college35.7 (53)37.7 (70)36.8
    College graduation or higher36.2 (50)44.5 (35)39.6
Full-term pregnancies
    >243.3 (209)43.7 (124)43.50.01
    ≤238.6 (120)39.2 (110)38.9
Age at first full-term pregnancy
    <3042.3 (269)42.7 (173)41.90.50
    ≥3041.4 (60)38.6 (61)40.4
Age at menarche
    >1242.0 (179)41.3 (101)41.70.89
    ≥1241.1 (150)41.8 (133)41.5
BMI
    <2534.5 (47)33.2 (48)33.80.0005
    25-29.945.7 (121)44.3 (71)45.2
    30-3541.7 (86)42.6 (59)42.1
    >3539.3 (75)44.3 (56)41.4
History of hormone therapy use
    Yes39.4 (124)37.9 (103)38.70.01
    No42.9 (201)44.4 (126)43.5
Age at menopause
    <5045.3 (99)39.1 (65)42.80.15
    ≥5038.3 (55)39.0 (46)38.7
  • * Ps reported are the significance levels for association between ancestry and the risk factor, using ANOVA and adjusting for case/control status. There were no significant interaction terms among case/control status, genetic ancestry, and any of these risk factors.

  • Age at natural or surgical menopause.