Table 1.
Characteristics of study participants
| All WECARE participants (n=2107) | Subset of WECARE participants in present study (n=1806)* |
|||
|---|---|---|---|---|
| Characteristic | Bilateral breast cancer (cases,n=708) |
Unilateral breast cancer (controls,n=1399)† |
Bilateral breast cancer (cases,n=606) |
Unilateral breast cancer (controls,n=1200)† |
| MATCHING CHARACTERISTICS | ||||
| (n and % except where noted) | ||||
| Registry | ||||
| Iowa | 113 (16%) | 222 (16%) | 88 (15%) | 172 (14%) |
| Orange and San Diego Counties, California | 118 (17%) | 231 (17%) | 99 (16%) | 194 (16%) |
| Los Angeles County, California | 199 (28%) | 390 (28%) | 175 (29%) | 343 (29%) |
| Seattle, Washington | 99 (14%) | 198 (14%) | 83 (14%) | 169 (14%) |
| Denmark | 179 (25%) | 358 (26%) | 161 (27%) | 322 (27%) |
| Race | ||||
| White | 649 (92%) | 1288 (92%) | 550 (91%) | 1096 (91%) |
| White of Spanish surname | 24 (3%) | 48 (3%) | 22 (4%) | 43 (4%) |
| Black | 21 (3%) | 39 (3%) | 20 (3%) | 37 (3%) |
| Asian | 6 (1%) | 8 (1%) | 6 (1%) | 8 (1%) |
| Filipino | 7 (1%) | 14 (1%) | 7 (1%) | 14 (1%) |
| Other | 1 (<1%) | 2 (<1%) | 1 (<1%) | 2 (<1%) |
| 1st Breast cancer diagnosis (y) | ||||
| 1985 – 1989 | 303 (43%) | 580 (41%) | 260 (43%) | 492 (41%) |
| 1990 – 1995 | 317 (45%) | 638 (46%) | 269 (44%) | 558 (47%) |
| 1996 – 1999 | 88 (12%) | 181 (13%) | 77 (13%) | 150 (13%) |
| Mean age (y) at first breast cancer (range) | 46 (24 – 55) | 46 (23 – 55) | 46 (24 – 55) | 46 (23 – 55) |
| Mean age (y) at reference date (range)‡ | 51 (27– 71) | 51 (27– 69) | 51 (28 – 71) | 51 (27 – 69) |
| Mean at-risk period (y) (range) | 5 (1 – 16) | 5 (1 – 16) | 5 (1 – 16) | 5 (1 – 16) |
| TREATMENT CHARACTERISTICS | ||||
| (primary / recurrent breast cancer) | ||||
| Radiation§ | ||||
| No | 362 (51%) | 266 (50%) | 302 (50%) | 238 (51%) |
| Yes | 346 (49%) | 1133 (50%) | 304 (50%) | 962 (49%) |
| Chemotherapy | ||||
| No | 386 (55%) | 629 (43%) | 330 (54%) | 546 (44%) |
| Yes | 322 (45%) | 770 (58%) | 276 (46%) | 654 (56%) |
| Radiation and chemotherapy | ||||
| No | 541 (76%) | 779 (71%) | 464 (77%) | 677 (72%) |
| Yes | 167 (24%) | 620 (29%) | 142 (23%) | 523 (28%) |
| Hormone therapy | ||||
| No | 511 (72%) | 909 (66%) | 447 (74%) | 774 (66%) |
| Yes | 197 (28%) | 488 (34%) | 159 (26%) | 424 (34%) |
| Unknown | 0 (0%) | 2 (<1%) | 0 (0%) | 2 (<1%) |
| Mastectomy | ||||
| No | 258 (36%) | 851 (36%) | 231 (38%) | 717 (35%) |
| Yes (total or partial) | 450 (64%) | 548 (64%) | 375 (62%) | 483 (65%) |
| OTHER CHARACTERISTICS | ||||
| Age at menarche | ||||
| 8 −13 years | 338 (48%) | 611 (41%) | 289 (48%) | 525 (41%) |
| 13+ years | 367 (52%) | 782 (58%) | 315 (52%) | 670 (58%) |
| Unknown | 3 (<1%) | 6 (1%) | 2 (<1%) | 5 (1%) |
| Age at menopause (as of reference date) | ||||
| Premenopausal | 124 (18%) | 273 (18%) | 104 (17%) | 227 (18%) |
| <45 years | 209 (30%) | 455 (34%) | 186 (31%) | 385 (34%) |
| 45–54 years | 374 (53%) | 665 (47%) | 316 (52%) | 584 (47%) |
| Unknown | 1 (<1%) | 6 (1%) | 0 (0%) | 4 (1%) |
| Nulliparous at reference age | ||||
| No | 575 (81%) | 1172 (84%) | 492 (81%) | 1003 (83%) |
| Yes | 133 (19%) | 225 (16%) | 114 (19%) | 195 (17%) |
| Unknown | 0 (0%) | 2 (<1%) | 0 (0%) | 2 (<1%) |
| Number of full-term pregnancies | ||||
| None | 133 (19%) | 225 (16%) | 114 (19%) | 195 (17%) |
| 1 | 121 (17%) | 204 (15%) | 104 (17%) | 170 (15%) |
| 2 | 270 (38%) | 545 (36%) | 229 (38%) | 463 (36%) |
| 3 | 128 (18%) | 263 (22%) | 111 (18%) | 225 (22%) |
| 4 or more | 56 (8%) | 160 (11%) | 48 (8%) | 145 (11%) |
| Unknown | 0 (0%) | 2 (<1%) | 0 (0%) | 2 (<1%) |
| Family history of breast cancer | ||||
| Adopted (family history unknown) | 11 (2%) | 26 (2%) | 10 (2%) | 22 (2%) |
| None | 472 (67%) | 1088 (78%) | 408 (67%) | 933 (78%) |
| Any first-degree female relative | 225 (32%) | 285 (20%) | 188 (31%) | 245 (20%) |
| FIRST PRIMARY BREAST CANCER | ||||
| CHARACTERISTICS | ||||
| Histology | ||||
| Ductal | 505 (71%) | 1048 (76%) | 438 (72%) | 902 (76%) |
| Lobular | 90 (13%) | 131 (9%) | 69 (11%) | 112 (8%) |
| Medullary | 33 (5%) | 51 (3%) | 32 (5%) | 41 (3%) |
| Other | 79 (11%) | 165 (12%) | 66 (11%) | 141 (12%) |
| Unknown | 1 (<1%) | 4 (1%) | 1 (<1%) | 4 (1%) |
| Stage | ||||
| Localized | 506 (71%) | 916 (64%) | 434 (72%) | 784 (65%) |
| Regional | 202 (29%) | 483 (36%) | 172 (28%) | 416 (35%) |
| Estrogen receptor status | ||||
| Positive | 338 (48%) | 746 (54%) | 287 (47%) | 658 (55%) |
| Negative | 193 (27%) | 338 (24%) | 168 (28%) | 274 (23%) |
| Unknown | 177 (25%) | 315 (22%) | 151 (25%) | 268 (23%) |
| Progesterone receptor status | ||||
| Positive | 287 (41%) | 616 (43%) | 233 (38%) | 536 (44%) |
| Negative | 172 (24%) | 318 (24%) | 157 (26%) | 262 (23%) |
| Unknown | 249 (35%) | 465 (33%) | 216 (36%) | 402 (34%) |
*
Cases for whom information on location of the tumor and dose were available and their matched controls.
†
Proportions estimated accounting for counter-matched sampling.
‡
Reference date for the cases is defined as the diagnosis date of the second primary; for the controls it is defined as the date of the first breast cancer diagnosis plus the “at-risk interval” of matched case.
§
Actual RT as determined by medical records and interviews. Counter-matching was based only on registry-recorded RT information, which may not be the same as actual RT information.