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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