Table 4.

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

0–68% NA Ancestry69–100% NA Ancestry
Risk factorsCases (n = 236)Controls (n = 232)OR (95% CI)aCases (n = 190)Controls (n = 269)OR (95% CI)aPinteraction
Ageb, y1.06 (1.02–1.09)1.02 (1.00–1.05)0.27
Family history of breast cancer, No. (%)0.36
 Yes21 (8.9)10 (4.2)2.53 (1.10–5.85)8 (4.2)2 (0.7)5.57 (1.15–27.01)
 No215 (91.1)222 (95.7)Referent182 (95.8)267 (99.3)Referent
No. births and age at first birthc, No. (%)0.14
 Nulliparous31 (13.1)7 (3.0)3.60 (1.22–10.61)20 (10.5)15 (5.6)2.48 (0.946.60)
 1–2, <25 y21 (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 y44 (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 y101 (42.8)154 (66.4)Referent100 (52.6)162 (60.2)Referent
 ≥3, ≥25 y39 (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. (%)d0.06
 None63 (26.7)29 (12.5)2.19 (0.994.86)37 (19.5)43 (16.0)1.06 (0.47–2.39)
 ≤12140 (59.3)140 (60.3)1.35 (0.77–2.37)120 (63.2)160 (59.5)1.42 (0.84–2.42)
 >1233 (14.0)63 (27.2)Referent33 (17.4)66 (24.5)Referent
Ptrend = 0.06Ptrend = 0.61
Body mass indexb, kg/m2, No. (%)0.43
 <25.043 (18.2)27 (11.7)Referent25 (13.2)31 (11.5)Referent
 25.0, 29.990 (38.1)75 (32.3)0.77 (0.41–1.44)77 (40.5)106 (39.4)0.89 (0.48–1.66)
 ≥30103 (43.6)130 (56.0)0.53 (0.29–0.97)88 (46.3)132 (49.1)0.82 (0.44–1.51)
Ptrend = 0.02Ptrend = 0.51
Age at menarche, y, No. (%)0.75
 ≤1146 (19.5)37 (16.0)1.62 (0.89–2.94)38 (20.0)54 (20.1)1.33 (0.75–2.33)
 12–13115 (48.7)101 (43.5)1.37 (0.87–2.15)100 (52.6)118 (43.9)1.52 (0.972.38)
 ≥1475 (31.8)94 (40.5)Referent52 (27.4)97 (36.0)Referent
Ptrend = 0.09Ptrend = 0.23
Age at menopause, y, No. (%)0.46
 ≤50158 (67.0)152 (65.5)Referent131 (69.0)189 (70.3)Referent
 >5078 (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
 Ever66 (28.0)33 (14.2)1.94 (1.16–3.26)36 (18.9)39 (15.2)1.17 (0.70–1.96)
 Never170 (72.0)199 (85.8)Referent154 (81.1)228 (84.8)Referent
Alcohol consumptionb,e No. (%)0.11
 None189 (80.1)219 (94.4)Referent167 (87.9)249 (92.6)Referent
 Any47 (19.9)13 (5.6)3.61 (1.77–7.36)23 (12.1)20 (7.4)1.62 (0.84–3.12)
  • NOTE: Results in bold are significant; results in italics are marginally significant.

    Abbreviations: CI, confidence interval; OR, odds ratio.

  • aAdjusted for all listed factors as well as study site.

  • bIn referent year.

  • cIncludes live or still birth.

  • dIncludes both parous and nonparous women.

  • eAlcohol consumption was based on lifetime average intake (4-Corners and Mexico subjects) or intake during the reference year (SFBCS).