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. 2013 Mar 18;4(1):35–48.

Table 1.

Characteristics of selected cases (CBC) and controls (UBC) from the WECARE Study population1

Cases (CBC) Controls (UBC)
Variable Median (Range) Median (Range) Median (Range)
Age at first Diagnosis (years) 46 (23-55) 46 (24-55) 46 (23-55)
Age at reference date (years) 51 (27-71) 50 (27-71) 51 (27-69)
Length of at-risk period2 (years) 4 (1-16) 4 (1-16) 4 (1-16)
  Cases (CBC) Controls (UBC)
Variable Level N % N %
Center Iowa 106 17 204 17
UC Irvine 101 16 189 16
Los Angeles 148 24 282 24
Seattle 93 15 185 15
Denmark 176 28 339 28
Year of first diagnosis 1985-88 217 35 415 35
1989-92 209 33 406 34
1993-96 157 25 300 25
1997+ 41 7 78 7
Chemotherapy No 347 56 548 46
Yes 277 44 651 54
Tamoxifen treatment No 485 78 861 72
Yes 139 22 338 28
Other hormonal treatment3 No 607 97 1150 96
Yes 17 3 48 4
Unknown 0 0 1 0.1
Radiation treatment4 Never 313 50 232 19
Ever 311 50 967 81
Histology of first breast cancer Lobular 81 13 118 10
Other 543 87 1081 90
Stage of first breast cancer Localized 447 72 776 65
Regional 177 28 423 35
ER Status of first breast cancer5 Positive 296 47 635 53
Negative 162 26 287 24
Other 166 27 277 23
PR Status of first breast cancer5 Positive 248 40 519 43
Negative 141 23 267 22
Other 235 38 413 34
Menopausal status/age at menopause at first diagnosis Premenopausal 460 74 905 75
Postmenopausal age <45 83 13 175 15
Postmenopausal age ≥45 80 13 115 10
Unknown 1 0.2 4 0.3
Family history of breast cancer None 415 67 935 78
≥1 first-degree relative 198 32 240 20
Adopted 11 2 24 2

Abbreviations: CBC=asynchronous contralateral breast cancer; UBC=unilateral breast cancer; ER=estrogen receptor, PR=progesterone receptor.

1

Includes Caucasian women with SNP call rates ≥95%, without significant African or Asian ancestry with complete information on tamoxifen treatment and genotype data from both the Omni1-Quad and custom BeadChip platforms (624 CBC cases and 1,199 UBC controls).

2

Beginning one year after first diagnosis extending to the reference date (date of second diagnosis in cases).

3

Other hormone therapies include raloxifene, toremifene citrate, anastrozole, letrozole, exemestane, aminoglutethimide, goserelin acetate, leuprorelin, fulvestrant and megestrol acetate.

4

CBC cases and UBC controls were counter-matched on registry-reported radiation treatment status.

For each radiation exposed case, one exposed and one unexposed control were selected from the relevant stratum, and for each unexposed case, two unexposed controls were selected. This is reflected in the percentages of cases and controls who underwent radiation treatment and was taken into account in all analyses.

5

Refers to receptor status of the first primary breast cancer.

The ‘Other’ category consists of women for whom no lab test was given, the test was given and the results are unknown or the test was given and the results were borderline.