Table 2.
Association between tumor characteristics of first primary breast cancer and contralateral breast cancer risk
| First primary breast cancer | Cases, N (%) | Controls, N (%) | RRa (95% CI) |
|---|---|---|---|
| Histology | |||
| Non-lobular | 1338 (88) | 1986 (90) | 1.0 (ref.) |
| Lobular | 179 (12) | 223 (10) | 1.3 (1.0, 1.6) |
| Unknown | 4 (0) | 3 (0) | |
| Grade | |||
| Well | 248 (16) | 338 (15) | 1.0 (ref.) |
| Moderate | 417 (27) | 688 (31) | 0.8 (0.7, 1.1) |
| Poor/undifferentiated | 503 (33) | 640 (29) | 1.1 (0.8, 1.4) |
| Unknown | 353 (23) | 546 (25) | |
| Stage | |||
| Localized | 1061 (70) | 1442 (65) | 1.0 (ref.) |
| Regional | 448 (29) | 759 (34) | 1.0 (0.9, 1.2) |
| Unknown | 12 (1) | 11 (1) | |
| Lymph node status | |||
| Negative | 1045 (69) | 1426 (64) | 1.0 (ref.) |
| Positive | 438 (29) | 751 (34) | 1.0 (0.8, 1.2) |
| No nodes sampled | 22 (2) | 26 (1) | 1.3 (0.7, 2.4) |
| Unknown | 16 (1) | 9 (0) | |
| Tumor size | |||
| ≤10 mm | 335 (22) | 510 (23) | 1.0 (ref.) |
| >10 to ≤20 mm | 595 (39) | 913 (41) | 1.1 (0.9, 1.3) |
| >20 mm | 477 (31) | 662 (30) | 1.1 (0.9, 1.4) |
| Inflammatory | 6 (0) | 2 (0) | |
| Unknown | 108 (7) | 125 (6) | |
| ER status | |||
| Positive | 797 (52) | 1254 (57) | 1.0 (ref.) |
| Negative | 467 (31) | 561 (25) | 1.3 (1.1, 1.6) |
| Other/unknownb | 257 (17) | 397 (18) | |
| PR status | |||
| Positive | 687 (45) | 1083 (49) | 1.0 (ref.) |
| Negative | 442 (29) | 549 (25) | 1.2 (1.0, 1.5) |
| Other/unknownb | 392 (26) | 580 (26) | |
| Joint ER/PR status | |||
| ER+/PR+ | 621 (41) | 958 (43) | 1.0 (ref.) |
| ER+/PR- | 85 (6) | 142 (6) | 1.0 (0.7, 1.4) |
| ER-/PR- | 352 (23) | 387 (18) | 1.4 (1.1, 1.7) |
| Other/unknownb,c | 463 (30) | 725 (33) | |
| HER2 statusd | |||
| Negative | 207 (25) | 222 (27) | 1.0 (ref.) |
| Positive | 53 (7) | 63 (8) | 0.8 (0.5, 1.3) |
| Unknownb | 553 (68) | 528 (65) | |
| Triple-negatived | |||
| No | 514 (63) | 579 (71) | 1.0 (ref.) |
| Yes | 59 (7) | 40 (5) | 1.3 (0.8, 2.2) |
| Other/unknownb | 240 (30) | 194 (24) | |
Abbreviations: RR risk ratio, CI confidence interval, N number, ER estrogen receptor, PR progesterone receptor, HER2 human epidermal growth factor receptor 2. aAdjusted for age at first breast cancer diagnosis, first-degree family history of breast cancer, histologic assessment, menopausal status, age at menarche, parity, radiation, chemotherapy and hormone therapy at first breast cancer diagnosis. Model examining histology was not adjusted for histologic assessment. b“Other/unknown” category consists of women for whom no laboratory test was given, the test was given and the results were unknown or the test was given and the results were borderline; estimates not reported. The start date for ER/PR reporting in SEER was 1 January 1990 [47]. cIncludes 59 cases and 108 controls classified as ER-/PR+. dAmong participants in the Women’s Environmental Cancer and Radiation Epidemiology II Study (WECARE II) only; HER2 status not queried for WECARE I participants. Surveillance, Epidemiology, and End Results (SEER) Registry only began collecting HER2 status in 2010 [46]