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Table 1 Characteristics of cases and controls from the WECARE Study population

From: Hormone receptor status of a first primary breast cancer predicts contralateral breast cancer risk in the WECARE study population

Variable CBC cases
N = 1521
UBC controls
N = 2212
Age at first diagnosis (years), median (range) 46 (24-54) 46 (23-54)
Age at reference date (years), median (range) 53 (27-73) 52 (27-71)
Length of at-risk period (years)a, median (range) 6.3 (1.0-19.8) 5.5 (1.0-19.8)
Study area, N (%)
 Iowab
 Californiac
 Seattled
 Denmarke
 Canadaf
201 (13)
658 (43)
224 (15)
279 (18)
159 (10)
314 (14)
967 (44)
317 (14)
457 (21)
157 (7)
Year of first breast cancer diagnosis, N (%)
 1985–1988
 1989–1992
 1993–1996
 1997–2008
238 (16)
415 (27)
427 (28)
441 (29)
467 (21)
647 (29)
632 (29)
466 (21)
Age at menarche (years), N (%)
 Never had menses
 <13
 ≥13
 Unknown
3 (0)
724 (48)
791 (52)
3 (0)
6 (0)
965 (44)
1239 (56)
2 (0)
Number of full-term pregnancies, N (%)
 None
 1
 2
 3
 ≥4
 Unknown
322 (21)
271 (18)
559 (37)
256 (17)
108 (7)
5 (0)
412 (19)
341 (15)
842 (38)
387 (17)
225 (10)
5 (0)
Menopausal statusg, N (%)
 Premenopausal
 Postmenopausal
 Unknown
1124 (74)
389 (26)
8 (1)
1676 (76)
522 (24)
14 (1)
First-degree family history of breast cancer, N (%)
 No
 Yes
 Adopted/unknown
1004 (66)
497 (33)
20 (1)
1706 (77)
466 (21)
40 (2)
Stage of first diagnosis, N (%)
 Local
 Regional
 Unknown
1061 (70)
448 (29)
12 (1)
1442 (65)
759 (34)
11 (1)
Chemotherapy, N (%)
 No
 Yes
699 (46)
822 (54)
923 (42)
1289 (58)
Radiation treatment, N (%)
 No
 Yes
 Unknown
641 (42)
880 (58)
0 (0)
522 (24)
1689 (76)
1 (0)
BRCA1/2 deleterious mutations, N (%)
 No 596 (39) 1322 (60)
 Yes 109 (7) 76 (3)
 Not testedh 816 (54) 814 (37)
Hormone treatment, N (%)
 No
 Yes
 Unknown
964 (63)
557 (37)
0 (0)
1270 (57)
940 (42)
2 (0)
  1. Abbreviations: WECARE Women’s Environmental Cancer and Radiation Epidemiology Study, CBC contralateral breast cancer, UBC unilateral breast cancer. aBeginning at least one year after first diagnosis and extending to the date of CBC diagnosis of cases. bThe State Health Registry of Iowa. cFour study centers: (1) Los Angeles County Cancer Surveillance Program, (2) The Cancer Surveillance Program of Orange County/San Diego-Imperial Organization for Cancer Control, (3) Greater Bay Area Cancer Registry (San Francisco Bay Area Region and Santa Clara Region), and (4) Sacramento and Sierra Center Registry (Sacramento Region). dCancer Surveillance System of the Fred Hutchinson Cancer Research Center. eThe Danish Breast Cancer Cooperative Group Database supplemented by the Danish Cancer Registry. fThe Ontario Cancer Registry. gWomen were classified as premenopausal if they reported having menstrual periods or being pregnant within 2 years of initial diagnosis. hOnly WECARE I Study participants were screened for BRCA1/2 deleterious mutations