Table 1.

Multivariate adjusted case-control odds ratios and 95% CIs for all breast cancer cases, triple-negative and non-triple-negative cases, in relation to known and suspected risk factors among women 45 y of age and younger, 1983-1992

Triple-negative status
P*
Controls (n = 1,569)

All breast cancer (n = 897)
Triple-negative (n = 187)
Non-triple-negative (n = 710)
n(%)n(%)OR(95% CI)n(%)OR(95% CI)n(%)OR(95% CI)
Demographic/lifestyle factors
Age (y)
    <30155(9.9)35(3.9)1.0Reference9(4.8)1.0Reference26(3.7)1.0Reference
    30-34297(18.9)140(15.6)2.1(1.1-3.9)38(20.3)2.6(0.8-9.1)102(14.4)2.0(1.0-3.9)
    35-39573(36.5)335(37.3)2.4(1.3-4.3)79(42.2)2.9(0.9-9.8)256(36.1)2.2(1.2-4.2)
    40-45544(34.7)387(43.1)2.6(1.4-4.6)61(32.6)2.2(0.7-7.4)326(45.9)2.7(1.4-5.1)
    P for trend0.0060.810.0020.13
Race
    White1,482(94.6)836(93.7)1.0Reference178(95.7)1.0Reference658(93.2)1.0Reference
    Black27(1.7)20(2.2)0.9(0.4-2.5)3(1.6)0.0N/A17(2.4)1.2(0.5-3.2)
    Other58(3.7)36(4.0)0.9(0.5-1.7)5(2.7)0.9(0.3-3.1)31(4.4)0.9(0.4-1.8)0.05
Education
    <College graduate1,035(66.0)572(63.8)1.0Reference119(63.6)1.0Reference453(63.8)1.0Reference
    College graduate533(34.0)325(36.2)1.2(1.0-1.6)68(36.4)1.3(0.9-2.0)257(36.2)1.2(1.0-1.6)0.61
Annual income
    <15,000184(11.9)81(9.1)1.0Reference14(7.5)1.0Reference67(9.5)1.0Reference
    15,000-45,000/50,000863(55.9)471(52.9)1.3(0.8-1.9)99(52.9)1.2(0.6-2.6)372(52.9)1.3(0.8-1.9)
    45,000/50,000+496(32.1)338(38.0)1.3(0.8-1.9)74(39.6)1.5(0.7-3.2)264(37.6)1.2(0.8-1.9)
    P for trend0.390.240.640.55
Family history of breast cancer
    None807(67.8)363(50.3)1.0Reference78(47.6)1.0Reference285(51.1)1.0Reference
    1st degree95(8.0)150(20.8)3.0(2.1-4.1)37(22.6)3.5(2.1-5.9)113(20.3)2.8(2.0-4.0)
    2nd degree only289(24.3)209(28.9)1.7(1.3-2.2)49(29.9)1.8(1.2-2.8)160(28.7)1.7(1.3-2.2)0.70
BMI (k/m2)§
    <18.587(5.6)35(4.0)0.7(0.4-1.2)6(3.2)0.5(0.2-1.7)29(4.2)0.8(0.4-1.4)
    18.5-24.9977(63.4)578(65.6)1.0Reference121(65.1)1.0Reference457(65.8)1.0Reference
    25.0-29.9269(17.4)151(17.1)1.0(0.7-1.3)33(17.7)1.1(0.6-1.8)118(17.0)0.9(0.7-1.3)
    30+209(13.6)117(13.3)0.9(0.7-1.3)26(14.0)1.3(0.8-2.2)91(13.1)0.8(0.6-1.2)
    P for trend0.990.180.540.12
Smoking
    Never801(51.4)464(52.2)1.0Reference100(54.6)1.0Reference364(51.6)1.0Reference
    Former332(21.3)189(21.3)0.9(0.7-1.2)34(18.6)0.8(0.5-1.3)155(22.0)0.9(0.7-1.3)
    Current424(27.2)236(26.5)0.9(0.7-1.2)49(26.8)1.0(0.6-1.6)187(26.5)0.9(0.7-1.2)0.29
Alcohol use (drinks/wk)
    None/<1771(49.2)442(49.3)1.0Reference88(47.1)1.0Reference354(49.9)1.0Reference
    1-3288(18.4)152(17.0)1.0(0.7-1.3)29(15.5)0.8(0.5-1.4)123(17.3)1.0(0.7-1.4)
    3+507(32.4)302(33.7)1.1(0.9-1.4)70(37.4)1.1(0.7-1.6)232(32.7)1.1(0.8-1.4)
    P for trend0.540.840.540.49
Reproductive factors
Age at menarche (y)
    8-12737(47.1)471(52.5)1.0Reference98(52.4)1.0Reference373(52.5)1.0Reference
    13-14690(44.1)351(39.1)0.8(0.6-1.0)77(41.2)0.8(0.6-1.2)274(38.6)0.7(0.6-1.0)
    15+139(8.9)75(8.4)0.8(0.5-1.2)12(6.4)0.4(0.2-1.0)63(8.9)0.9(0.6-1.4)
    P for trend0.030.050.110.33
Number of live births
    None396(25.2)232(25.9)1.0Reference53(28.3)1.0Reference179(25.2)1.0Reference
    1-31,057(67.4)621(69.2)0.8(0.5-1.3)127(67.9)0.9(0.4-1.9)494(69.6)0.8(0.5-1.3)
    4+116(7.4)44(4.9)0.5(0.3-1.0)7(3.7)0.6(0.2-1.9)37(5.2)0.5(0.3-1.0)
    P for trend0.040.380.040.83
Age at first birth (y)
    None390(24.9)230(25.7)1.0Reference53(28.3)1.0Reference177(25.0)1.0Reference
    <20264(16.8)116(12.9)0.6(0.3-1.0)19(10.2)0.6(0.2-1.4)97(13.7)0.6(0.3-1.0)
    20-29745(47.5)419(46.8)0.8(0.5-1.3)86(46.0)0.9(0.4-2.0)333(47.0)0.8(0.5-1.3)
    30+170(10.8)131(14.6)1.0(0.6-1.8)29(15.5)1.2(0.5-3.0)102(14.4)1.0(0.6-1.8)
    P for trend0.0020.030.0090.49
Lactation**
    Never313(26.9)189(28.5)1.0Reference33(24.6)1.0Reference156(29.4)1.0Reference
    <12494(42.5)279(42.0)1.1(0.8-1.4)63(47.0)1.1(0.7-1.8)216(40.8)1.1(0.8-1.5)
    12+356(30.6)196(29.5)1.0(0.7-1.4)38(28.4)1.0(0.6-1.7)158(29.8)1.0(0.7-1.4)
    P for trend0.970.990.980.78
Abortion††
    Never950(72.9)510(67.3)1.0Reference98(64.5)1.0Reference412(68.0)1.0Reference
    Ever354(27.1)248(32.7)1.4(1.1-1.8)54(35.5)1.4(0.9-2.2)194(32.0)1.4(1.1-1.8)0.82
Oral contraception
OC use (y)
    Never/<1407(25.9)197(22.0)1.0Reference22(11.8)1.0Reference175(24.7)1.0Reference
    1+1,162(74.1)699(78.0)1.3(1.0-1.7)165(88.2)2.5(1.4-4.3)534(75.3)1.2(0.9-1.5)0.008
OC duration (y)‡‡
    1 to <3327(20.8)184(20.5)1.3(0.9-1.7)35(18.7)1.6(0.9-3.3)149(21.0)1.2(0.9-1.7)
    3 to <6357(22.8)220(24.6)1.4(1.0-2.0)51(27.3)2.8(1.5-5.3)169(23.8)1.2(0.9-1.7)
    6+478(30.5)295(32.9)1.3(1.0-1.8)79(42.2)2.9(1.6-5.3)216(30.5)1.1(0.8-1.5)
    P for trend0.850.050.450.02
Age at first use (y)‡‡
    22+260(16.6)159(17.7)1.2(0.9-1.7)31(16.6)2.0(1.0-4.1)128(18.1)1.1(0.8-1.6)
    18 to <22674(43.0)390(43.5)1.2(0.9-1.6)92(49.2)2.3(1.3-4.1)298(42.0)1.1(0.8-1.4)
    <18228(14.5)150(16.7)1.9(1.3-2.7)42(22.5)3.7(1.9-7.2)108(15.2)1.6(1.1-2.3)
    P for trend0.050.130.100.84
Years since first use‡‡
    1 to <15313(19.9)132(14.7)1.3(0.8-1.9)36(19.3)2.4(1.1-5.1)96(13.5)1.1(0.7-1.6)
    15 to <20462(29.4)277(30.9)1.3(1.0-1.8)78(41.7)3.0(1.6-5.4)199(28.1)1.1(0.8-1.5)
    20+387(24.7)290(32.4)1.4(1.0-1.9)51(27.3)2.0(1.1-4.0)239(33.7)1.3(0.9-1.8)
    P for trend0.270.740.250.74
Years since last use‡‡
    Current120(7.6)43(4.8)1.0(0.6-1.8)16(8.6)3.1(1.2-7.6)27(3.8)0.7(0.4-1.4)
    1 to <5190(12.1)116(12.9)1.9(1.3-2.9)31(16.6)4.2(2.0-8.6)85(12.0)1.6(1.1-2.5)
    5 to <10255(16.3)136(15.2)1.2(0.8-1.7)41(21.9)3.0(1.6-5.9)95(13.4)0.9(0.6-1.3)
    10 to <15339(21.6)213(23.8)1.3(1.0-1.8)55(29.4)2.6(1.4-4.8)158(22.3)1.2(0.8-1.6)
    15+258(16.4)191(21.3)1.3(0.9-1.8)22(11.8)1.2(0.6-2.6)169(23.8)1.3(0.9-1.8)
    P for trend0.860.040.390.01
  • NOTE: Risk factors adjusted for age, family history of breast cancer, breastfeeding history, and oral contraceptive duration.

    Abbreviations: OR, odds ratio; OC, oral contraceptive.

  • * Pheterogeneity (association of risk factor with triple-negative versus non-triple-negative breast cancer).

  • Because of missing data, race was adjusted for age, breastfeeding history, and oral contraceptive duration but not family history of breast cancer.

  • Income categories reflect the fact that the two studies combined for the present study used different cutoffs.

  • § One year before reference date.

  • Still and live births.

  • P for trend among parous women only.

  • ** Among parous women.

  • †† Among gravid women.

  • ‡‡ Ptrend and Pheterogeneity among oral contraceptive users >1 year only.