Table 2.
Associations of tumor characteristics and treatment modes with primary breast cancer as the second malignancy (BCa-2): a SEER population-based study in US, 1990–2015
| BCa-1 | BCa-2 | ||
| N (%) | N (%) | OR (95% CI) a | |
| Histology | |||
| Ductal | 643,139 (72.8) | 25,487 (70.2) | 1.00 |
| Lobular | 73,112 (8.3) | 3456 (9.5) | 1.01 (0.97–1.05) |
| Mixed | 82,546 (9.3) | 3439 (9.5) | 1.02 (0.98–1.06) |
| Others | 85,084 (9.6) | 3931 (10.8) | 1.04 (1.00–1.08) |
| Tumor grade | |||
| Well differentiated | 165,869 (18.8) | 7817 (21.5) | 1.00 |
| Moderately differentiated | 337,563 (38.2) | 14,526 (40.0) | 0.97 (0.94–1.00) |
| Poorly differentiated | 277,729 (31.4) | 9435 (26.0) | 0.91 (0.88–0.94) |
| Undifferentiated | 9863 (1.1) | 266 (0.7) | 0.86 (0.76–0.98) |
| Tumor size | |||
| 0-2 cm | 506,784 (57.3) | 22,629 (62.3) | 1.00 |
| 2-5 cm | 260,786 (29.5) | 9608 (26.5) | 0.85 (0.83–0.87) |
| > 5 cm | 66,236 (7.5) | 1884 (5.2) | 0.67 (0.64–0.71) |
| Tumor stage | |||
| Local | 547,036 (61.9) | 24,624 (67.8) | 1.00 |
| Regional | 265,617 (30.1) | 8815 (24.3) | 0.86 (0.84–0.88) |
| Distant | 57,578 (6.5) | 2065 (5.7) | 0.79 (0.75–0.83) |
| Molecular subtypesc | |||
| HR+/HER2- | 205,424 (67.4) | 11,106 (70.4) | 1.00 |
| HR+/HER2+ | 30,893 (10.1) | 1283 (8.1) | 0.93 (0.88–0.99) |
| HR−/HER2+ | 13,507 (4.4) | 492 (3.1) | 0.82 (0.75–0.90) |
| Triple negative | 32,172 (10.6) | 1481 (9.4) | 1.00 (0.94–1.05) |
| N (%) | N (%) | OR (95% CI) b | |
| Surgery d | |||
| No | 60,648 (7.8) | 3712 (11.6) | 1.00 |
| Lumpectomy | 404,612 (52.3) | 17,372 (54.1) | 0.75 (0.72–0.79) |
| Mastectomy | 304,812 (39.4) | 10,900 (33.9) | 0.74 (0.71–0.78) |
| Chemotherapy | |||
| No/unknown | 536,470 (60.7) | 27,537 (75.8) | 1.00 |
| Yes | 347,411 (39.3) | 8776 (24.2) | 0.84 (0.81–0.86) |
| Radiotherapy | |||
| No/unknown | 462,215 (52.3) | 21,631 (59.6) | 1.00 |
| Yes | 421,666 (47.7) | 14,682 (40.4) | 0.83 (0.82–0.85) |
| Treatment modesd | |||
| Lumpectomy only | 79,295 (10.3) | 5149 (16.0) | 1.00 |
| Mastectomy only | 138,766 (17.9) | 6648 (20.7) | 0.88 (0.85–0.92) |
| Chemo−/radio-therapy | 27,038 (3.5) | 1038 (3.2) | 1.05 (0.97–1.13) |
| Lumpectomy plus chemo−/radio-therapy | 325,317 (42.1) | 12,223 (38.0) | 0.79 (0.76–0.82) |
| Mastectomy plus chemo−/radio-therapy | 166,046 (21.5) | 4252 (13.2) | 0.74 (0.71–0.78) |
| Otherse | 36,829 (4.8) | 2817 (8.8) | 1.16 (1.10–1.23) |
NOTE. Patients with missing information on tumor stage (N = 14,459, 1.57%), tumor grade (N = 97,126, 10.56%), tumor size (N = 52,267, 5.68%), molecular types (N = 24,220, 7.6%) or surgery (N = 3362, 0.4%) were not included in the corresponding analysis
Abbreviations: BCa-1 Breast cancer as the first malignancy, CI Confidence interval, HR Hormone-receptor, HER2 Human epidermal growth factor receptor 2, N Number; OR Odds ratio
a The models were adjusted for age (continuous) and calendar period at diagnosis, race, cohabitation status, percentile of cost of living and high-school education in county of residence
b The models were additionally adjusted for tumor stage, histology, tumor grade, ER status, PR status, and HER2 status
c Information on HER2 status was available from 2010 onward, and thus the analysis was restricted to patients diagnosed thereafter
d Information on surgery and therapy was available from 1998 onward, and thus the analysis was restricted to patients diagnosed thereafter
e Others included surgery (no/unknown), chemotherapy (no/unknown), and radiotherapy (no/unknown)