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. Author manuscript; available in PMC: 2018 May 1.
Published in final edited form as: Cancer Epidemiol Biomarkers Prev. 2016 Dec 8;26(5):692–701. doi: 10.1158/1055-9965.EPI-16-0721

Table 4.

Relationship between risk factors and breast cancer risk according to percent Native American ancestry among postmenopausal Mexican women

Risk Factors 0–68% Native American Ancestry 69–100% Native American Ancestry P interaction


Cases (n= 236) Controls (n =232) OR (95% CI)a Cases (n = 190) Controls (n = 269) OR (95% CI)a
Ageb, y 1.06 (1.02, 1.09) 1.02 (1.00, 1.05) 0.27
Family history of breast cancer, No. (%) 0.36
 Yes 21 (8.9) 10 (4.2) 2.53 (1.10, 5.85) 8 (4.2) 2 (0.7) 5.57 (1.15, 27.01)
 No 215 (91.1) 222 (95.7) Referent 182 (95.8) 267 (99.3) Referent
No. births and age at first birthc, No. (%) 0.14
 Nulliparous 31 (13.1) 7 (3.0) 3.60 (1.22, 10.61) 20 (10.5) 15 (5.6) 2.48 (0.94, 6.60)
 1–2, < 25 y 21 (8.9) 21 (9.1) 1.36 (0.66, 2.84) 23 (12.1) 31 (11.5) 1.16 (0.62, 2.18)
 1–2, ≥25 y 44 (18.6) 28 (12.1) 1.68 (0.91, 3.12) 29 (15.3) 30 (11.2) 1.54 (0.83, 2.87)
 ≥3, <25 y 101 (42.8) 154 (66.4) Referent 100 (52.6) 162 (60.2) Referent
 ≥3, ≥25 y 39 (16.5) 22 (9.5) 2.21 (1.17, 4.15) 18 (9.5) 31 (11.5) 0.93 (0.48, 1.81)
Breastfeeding, mos, No. (%)d 0.06
 None 63 (26.7) 29 (12.5) 2.19 (0.99, 4.86) 37 (19.5) 43 (16.0) 1.06 (0.47, 2.39)
 ≤12 140 (59.3) 140 (60.3) 1.35 (0.77, 2.37) 120 (63.2) 160 (59.5) 1.42 (0.84, 2.42)
 >12 33 (14.0) 63 (27.2) Referent 33 (17.4) 66 (24.5) Referent
Ptrend = 0.06 Ptrend = 0.61
Body mass indexb, kg/m2, No. (%) 0.43
 <25.0 43 (18.2) 27 (11.7) Referent 25 (13.2) 31 (11.5) Referent
 25.0, 29.9 90 (38.1) 75 (32.3) 0.77 (0.41, 1.44) 77 (40.5) 106 (39.4) 0.89 (0.48, 1.66)
 ≥30 103 (43.6) 130 (56.0) 0.53 (0.29, 0.97) 88 (46.3) 132 (49.1) 0.82 (0.44, 1.51)
Ptrend = 0.02 Ptrend = 0.51
Age at menarche, y, No. (%) 0.75
 ≤11 46 (19.5) 37 (16.0) 1.62 (0.89, 2.94) 38 (20.0) 54 (20.1) 1.33 (0.75, 2.33)
 12, 13 115 (48.7) 101 (43.5) 1.37 (0.87, 2.15) 100 (52.6) 118 (43.9) 1.52 (0.97, 2.38)
 ≥14 75 (31.8) 94 (40.5) Referent 52 (27.4) 97 (36.0) Referent
Ptrend = 0.09 Ptrend = 0.23
Age at menopause, y, No. (%) 0.46
 ≤50 158 (67.0) 152 (65.5) Referent 131 (69.0) 189 (70.3) Referent
 >50 78 (33.0) 80 (34.5) 0.70 (0.44, 1.11) 59 (32.0) 80 (29.7) 1.01 (0.66, 1.56)
Hormone therapy useb No. (%) 0.13
 Ever 66 (28.0) 33 (14.2) 1.94 (1.16, 3.26) 36 (18.9) 39 (15.2) 1.17 (0.70, 1.96)
 Never 170 (72.0) 199 (85.8) Referent 154 (81.1) 228 (84.8) Referent
Alcohol consumptionb,e 0.11
 No. (%) 189 (80.1) 219 (94.4) Referent 167 (87.9) 249 (92.6) Referent
 None Any 47 (19.9) 13 (5.6) 3.61 (1.77, 7.36) 23 (12.1) 20 (7.4) 1.62 (0.84, 3.12)

OR, odds ratio; CI, confidence interval. Results in bold are significant; results in italics are marginally significant.

a

Adjusted for all listed factors as well as study site.

b

In referent year.

c

Includes live or still birth.

d

Includes both parous and non-parous women.

e

Alcohol consumptionwas based on lifetime average intake (4-Corners and Mexico subjects), or intake during the reference year (SFBCS).