Table 1.

Characteristics of controls and contralateral breast cancer cases

CharacteristicControls (n = 727)Contralateral cases (n = 367)
n (%)n (%)
Demographic characteristics
    Age at first breast cancer diagnosis, y
        40–49137 (18.8)71 (19.3)
        50–59198 (27.2)97 (26.4)
        60–69223 (30.7)112 (30.5)
        70–79169 (23.2)87 (23.7)
    Age at reference date (age at contralateral breast cancer diagnosis for cases), y
        40–59218 (30.0)106 (28.9)
        60–69231 (31.8)117 (31.9)
        70–79210 (28.9)104 (28.3)
        80–8868 (9.4)40 (10.9)
    Year of first breast cancer diagnosis
        1990–1993263 (36.2)133 (36.2)
        1994–1997246 (33.8)122 (33.2)
        1998–2001164 (22.6)85 (23.2)
        2002–200554 (7.4)27 (7.4)
    Months between first breast cancer diagnosis and reference date
        6–1144 (6.1)23 (6.3)
        12–23108 (14.9)54 (14.7)
        24–59236 (32.5)116 (31.6)
        60–119261 (35.9)133 (36.2)
        ≥12078 (10.7)41 (11.2)
    Race/ethnicity
        Non-Hispanic White662 (91.3)336 (92.1)
        Asian/Pacific Islander28 (3.9)12 (3.3)
        African American19 (2.6)9 (2.5)
        Native American10 (1.4)5 (1.4)
        Hispanic White6 (0.8)3 (0.8)
        Missing22
Treatments for first primary breast cancer
    Received radiation therapy for first primary breast cancer
        No248 (34.1)131 (35.7)
        Yes479 (65.9)236 (64.3)
    Received chemotherapy for first primary breast cancer
        No534 (73.6)272 (74.5)
        Yes192 (26.4)93 (25.5)
        Missing12
Tumor Characteristics
    AJCC stage
        I495 (68.1)239 (65.1)
        II or III232 (31.9)128 (34.9)
    Lymph node involvement
        No558 (76.8)273 (74.4)
        Yes169 (23.2)94 (25.6)
    Tumor size, cm
        ≤1.0247 (34.8)116 (33.0)
        1.1–2.0315 (44.4)143 (40.7)
        >2.0148 (20.8)92 (26.2)
        Missing1716
Patient characteristics
    First -degree family history of breast cancer at first breast cancer diagnosis
        No512 (74.5)237 (70.5)
        Yes175 (25.5)99 (29.5)
        Missing4031
    No. of full-term pregnancies at first breast cancer diagnosis
        0105 (14.9)58 (16.4)
        1–2303 (42.9)156 (44.1)
        ≥3299 (42.3)140 (39.5)
        Missing2013
    BMI at first breast cancer diagnosis, kg/m2
        <25.0317 (44.4)133 (37.3)
        25.0–29.9213 (30.0)116 (32.5)
        ≥30.0183 (25.7)108 (30.3)
        Missing1410
    BMI at reference date, kg/m2
        <25.0254 (39.2)110 (35.4)
        25.0–29.9221 (34.1)95 (30.5)
        ≥30.0174 (26.7)106 (34.1)
        Missing7856
    Ever used menopausal hormone therapy at first breast cancer diagnosis
        Never343 (49.7)172 (50.9)
        Former72 (10.4)40 (11.8)
        Current estrogen user144 (20.9)71 (21.0)
        Current estrogen+progestin user131 (19.0)55 (16.3)
        Missing3729
  • Abbreviation: AJCC, American Joint Committee on Cancer.