Table 1.

Characteristics of 2,107 women with unilateral and bilateral breast cancer included in the WECARE study

Bilateral (N = 708)Unilateral (N = 1,399)
Matched characteristics
    Registry, n (%)
    Iowa113 (16)222 (16)
    Orange County/San Diego118 (17)231 (17)
    Los Angeles County199 (28)390 (28)
    Seattle99 (14)198 (14)
    Denmark179 (25)358 (26)
Race, n (%)
    Non-Hispanic white649 (91.7)1,288 (92.1)
    Hispanic white24 (3.3)48 (3.4)
    Black21 (3)39 (2.8)
    Chinese2 (0.3)3 (0.2)
    Japanese2 (0.3)4 (0.3)
    Filipino7 (1)14 (1)
    Other Asian2 (0.3)1 (0.1)
Subject's age at first breast cancer diagnosis, mean (range)46 (24, 55)45 (23, 55)
Age at reference date*, mean (range)50 (27, 70)50 (27, 69)
At-risk period, mean (range)5 (1, 16)5 (1, 16)
Counter-matched characteristics
Radiation treatment (registry), n (%)
    No or unknown415 (59)290 (21)
    Yes293 (41)1,109 (79)
Other characteristics
First-degree family history of breast cancer, n (%)
    Adopted or family history unknown11 (1)26 (2)
    No472 (67)1,088 (78)
    Yes225 (32)285 (20)
Number of mammograms in year before reference date*, n (%)
    041 (6)116 (8)
    1503 (71)959 (69)
    2101 (14)149 (11)
    3+19 (3)20 (1)
    Unknown44 (6)155 (11)
Histology of first breast cancer, n (%)
    Ductal and other585 (82)1,217 (87)
    Lobular90 (13)131 (9)
    Medullary33 (5)51 (4)
Stage of first breast cancer, n (%)
    Localized503 (71)911 (65)
    Regional205 (29)488 (35)
Chemotherapy, n (%)
    No386 (55)629 (45)
    Yes322 (45)770 (55)
Hormone therapy, n (%)
    No511 (72)909 (65)
    Yes197 (28)488 (35)
  • * Reference date is date of contralateral breast cancer diagnosis for cases and corresponding date for controls.