Table 1 Demographic and clinical characteristics of patients, stratified by the number of micrometastatic lymph nodes
Characteristics | Total | N1mi = 1 | N1mi = 2 | N1mi ≥ 3 | P value |
|---|---|---|---|---|---|
N | 27,032 | 22,463 | 3089 | 1480 | Â |
Age, years |  |  |  |  |  < 0.001 |
  < 40 | 1838 (6.8) | 1463 (6.5) | 250 (8.1) | 125 (8.4) |  |
 40–59 | 13,141 (48.6) | 10,813 (48.1) | 1567 (50.7) | 761 (51.4) |  |
  ≥ 60 | 12,053 (44.6) | 10,187 (45.4) | 1272 (41.2) | 594 (40.1) |  |
Race |  |  |  |  |  < 0.001 |
 White | 21,466 (79.4) | 17,954 (79.9) | 2398 (77.6) | 1114 (75.3) |  |
 Black | 2793 (10.3) | 2198 (9.8) | 379 (12.3) | 216 (14.6) |  |
 Other a | 2773 (10.3) | 2311 (10.3) | 312 (10.1) | 150 (10.1) |  |
Marital | Â | Â | Â | Â | 0.003 |
 Married | 16,130 (59.7) | 13,501 (60.1) | 1793 (58.0) | 836 (56.5) |  |
 Single b | 9822 (36.3) | 8094 (36.0) | 1147 (37.1) | 581 (39.3) |  |
 Unknown | 1080 (4.0) | 868 (3.9) | 149 (4.8) | 63 (4.3) |  |
Histological types | Â | Â | Â | Â | 0.038 |
 IDC | 21,070 (77.9) | 17,565 (78.2) | 2377 (77.0) | 1128 (76.2) |  |
 ILC | 2123 (7.9) | 1725 (7.7) | 254 (8.2) | 144 (9.7) |  |
 Other | 3839 (14.2) | 3173 (14.1) | 458 (14.8) | 208 (14.1) |  |
Grade |  |  |  |  |  < 0.001 |
 I | 5252 (19.4) | 4596 (20.5) | 496 (16.1) | 160 (10.8) |  |
 II | 12,950 (47.9) | 10,786 (48.0) | 1483 (48.0) | 681 (46.0) |  |
 III | 8167 (30.2) | 6578 (29.3) | 1013 (32.8) | 576 (38.9) |  |
 Unknown | 663 (2.5) | 503 (2.2) | 97 (3.1) | 63 (4.3) |  |
T stage |  |  |  |  |  < 0.001 |
 T1 | 15,986 (59.1) | 13,758 (61.2) | 1613 (52.2) | 615 (41.6) |  |
 T2 | 11,046 (40.9) | 8705 (38.8) | 1476 (47.8) | 865 (58.4) |  |
Type of surgery |  |  |  |  |  < 0.001 |
 BCS | 14,826 (54.8) | 12,768 (56.8) | 1522 (49.3) | 536 (36.2) |  |
 Mastectomy | 12,206 (45.2) | 9695 (43.2) | 1567 (50.7) | 944 (63.8) |  |
Type of axillary surgery |  |  |  |  |  < 0.001 |
 SLNB | 15,622 (57.8) | 14,293 (63.6) | 1176 (38.1) | 153 (10.3) |  |
 ALND | 11,410 (42.2) | 8170 (36.4) | 1913 (61.9) | 1327 (89.7) |  |
Radiation | Â | Â | Â | Â | 0.181 |
 Yes | 14,368 (53.2) | 11,995 (53.4) | 1598 (51.7) | 775 (52.4) |  |
 No/refused | 12,664 (46.8) | 10,468 (46.6) | 1491 (48.3) | 705 (47.6) |  |
Chemotherapy |  |  |  |  |  < 0.001 |
 Yes | 14,039 (51.9) | 11,021 (49.1) | 1913 (61.9) | 1105 (74.7) |  |
 No/unknown | 12,993 (48.1) | 11,442 (50.9) | 1176 (38.1) | 375 (25.3) |  |
ER status |  |  |  |  |  < 0.001 |
 Positive | 23,208 (85.9) | 19,446 (86.6) | 2593 (83.9) | 1169 (79.0) |  |
 Negative | 3271 (12.1) | 2586 (11.5) | 421 (13.6) | 264 (17.8) |  |
 Borderline | 553 (2.0) | 431 (1.9) | 75 (2.4) | 47 (3.2) |  |
PR status |  |  |  |  |  < 0.001 |
 Positive | 20,631 (76.3) | 17,285 (76.9) | 2315 (74.9) | 1031 (69.7) |  |
 Negative | 5649 (20.9) | 4584 (20.4) | 675 (21.9) | 390 (26.4) |  |
 Borderline | 752 (2.8) | 594 (2.6) | 99 (3.2) | 59 (4.0) |  |
HER2 status |  |  |  |  |  < 0.001 |
 Positive | 2048 (7.6) | 1690 (7.5) | 243 (7.9) | 115 (7.8) |  |
 Negative | 13,957 (51.6) | 12,044 (53.6) | 1409 (45.6) | 504 (34.1) |  |
 Borderline | 600 (2.2) | 488 (2.2) | 64 (2.1) | 48 (3.2) |  |
 Not 2010 +  | 10,427 (38.6) | 8241 (36.7) | 1373 (44.4) | 813 (54.9) |  |