Table 1. The characteristics of patients in the SEER database.
| Variables | All patients (n=9,914) | Training cohort (SEER-A; n=4,957) | Validation cohort (SEER-B; n=4,957) | P value |
|---|---|---|---|---|
| Sex, n (%) | ||||
| Male | 4,353 (43.9) | 2,180 (44.0) | 2,173 (43.8) | 0.887 |
| Female | 5,561 (56.1) | 2,777 (56.0) | 2,784 (56.2) | |
| Age at diagnosis (years), n (%) | ||||
| ≤65 | 4,202 (42.4) | 2,133 (43.0) | 2,069 (41.7) | 0.193 |
| >65 | 5,712 (57.6) | 2,824 (57.0) | 2,888 (58.3) | |
| Location of tumor, n (%) | ||||
| RUL | 3,548 (35.8) | 1,803 (36.4) | 1,745 (35.2) | 0.815 |
| RML | 545 (5.5) | 270 (5.4) | 275 (5.5) | |
| RLL | 1,795 (18.1) | 874 (17.7) | 921 (18.6) | |
| LUL | 2,544 (25.7) | 1,271 (25.6) | 1,273 (25.7) | |
| LLL | 1,390 (14.0) | 693 (14.0) | 697 (14.1) | |
| Others | 92 (0.9) | 46 (0.9) | 46 (0.9) | |
| Tumor size (cm), n (%) | ||||
| ≤1 | 821 (8.3) | 415 (8.4) | 406 (8.2) | 0.883 |
| 1–2 | 4,173 (42.1) | 2,084 (42.0) | 2,089 (42.1) | |
| 2–3 | 3,071 (31.0) | 1,539 (31.1) | 1,532 (30.9) | |
| 3–4 | 1,347 (13.6) | 660 (13.3) | 687 (13.9) | |
| 4–5 | 502 (5.0) | 259 (5.2) | 243 (4.9) | |
| Histologic type, n (%) | ||||
| ADC | 6,240 (63.0) | 3,089 (62.3) | 3,151 (63.6) | 0.049 |
| SCC | 2,334 (23.5) | 1,213 (24.5) | 1,121 (22.6) | |
| ASC | 196 (2.0) | 110 (2.2) | 86 (1.7) | |
| ACC | 568 (5.7) | 279 (5.6) | 289 (5.8) | |
| BAC | 131 (1.3) | 67 (1.4) | 64 (1.3) | |
| LCC | 151 (1.5) | 70 (1.4) | 81 (1.7) | |
| Others | 294 (3.0) | 129 (2.6) | 165 (3.3) | |
| Tumor grade, n (%) | ||||
| I | 2,356 (23.8) | 1,194 (24.1) | 1,162 (23.4) | 0.658 |
| II | 4,864 (49.1) | 2,429 (49.0) | 2,435 (49.2) | |
| III | 2,600 (26.2) | 1,292 (26.1) | 1,308 (26.4) | |
| IV | 94 (0.9) | 42 (0.8) | 52 (1.0) | |
| VPI, n (%) | ||||
| No | 8,898 (89.8) | 4,435 (89.5) | 4,463 (90.0) | 0.354 |
| Yes | 1,016 (10.2) | 522 (10.5) | 494 (10.0) | |
| Surgical approach, n (%) | ||||
| Sublobar resection | 1,403 (14.2) | 698 (14.1) | 705 (14.2) | 0.586 |
| Lobectomy | 8,411 (84.8) | 4,214 (85.0) | 4,197 (84.7) | |
| Pneumonectomy | 100 (1.0) | 45 (0.9) | 55 (1.1) | |
| Examined lymph nodes, n (%) | ||||
| ≥8 | 5,087 (51.3) | 2,514 (50.7) | 2,573 (51.9) | 0.236 |
| ≤7 | 4,827 (48.7) | 2,443 (49.3) | 2,384 (48.1) | |
| Race, n (%) | ||||
| White | 8,129 (82.0) | 4,072 (82.1) | 4,057 (81.8) | 0.104 |
| Black | 912 (9.2) | 429 (8.7) | 483 (9.8) | |
| Others | 832 (8.4) | 438 (8.8) | 394 (7.9) | |
| Unknown | 41 (0.4) | 18 (0.4) | 23 (0.5) |
P value was calculated by χ2 test. SEER, Surveillance Epidemiology and End Results; RUL, right upper lobe; RML, right middle lobe; RLL, right lower lobe; LUL, left upper lobe; LLL, left lower lobe; VPI, visceral pleural invasion; ADC, adenocarcinoma; SCC, squamous cell carcinoma; LCC, large cell carcinoma; ACC, acinar cell carcinoma; ASC, adeno-squamous carcinoma; BAC, bronchial alveolar carcinoma.