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).