| | Variables | Subgroup | No. (%) of patients | | Initial cohort (n = 3,111) | Training cohort (n = 1,886) | Validating cohort (n = 1,225) |
| | Age (year) | <45 | 286 (9.19) | 179 (9.49) | 107 (8.73) | | ≥45 and <60 | 790 (25.39) | 482 (25.56) | 308 (25.14) | | ≥60 and <70 | 942 (30.28) | 542 (28.74) | 400 (32.65) | | ≥70 | 1,093 (35.13) | 683 (36.21) | 410 (33.47) |
| | Race | White | 2,333 (74.99) | 1,435 (76.09) | 898 (73.31) | | Black | 378 (12.15) | 215 (11.40) | 163 (13.31) | | ※Others | 400 (12.86) | 236 (12.51) | 164 (13.39) |
| | Location | ¶Central | 219 (7.04) | 150 (7.95) | 69 (5.63) | | Upper | 1,329 (42.72) | 802 (42.52) | 527 (43.02) | | Lower | 680 (21.86) | 425 (22.53) | 255 (20.82) | | Axillary tail | 13 (0.42) | 10 (0.53) | 3 (0.24) | | Overlapping | 870 (27.97) | 499 (26.46) | 371 (30.29) |
| | ＆Grade | I | 1,897 (60.98) | 1,163 (61.66) | 734 (59.92) | | II | 1,107 (35.58) | 649 (34.41) | 458 (37.39) | | III | 107 (3.44) | 74 (3.92) | 33 (2.69) |
| | Laterality | Right | 1,487 (47.80) | 888 (47.08) | 599 (48.90) | | Left | 1,624 (52.20) | 998 (52.92) | 626 (51.10) |
| | ￥Stage | I | 2,120 (68.15) | 1,294 (68.61) | 826 (67.43) | | II | 962 (30.92) | 575 (30.49) | 387 (31.59) | | III | 29 (0.93) | 17 (0.90) | 12 (0.98) |
| | Tumor size (mm) | >0 and ≤5 | 225 (7.23) | 142 (7.53) | 83 (6.78) | | >5 and ≤10 | 663 (2.12) | 409 (21.69) | 254 (20.73) | | >10 and ≤20 | 1,290 (41.47) | 784 (41.57) | 506 (41.31) | | >20 and ≤50 | 933 (29.99) | 551 (29.21) | 382 (31.18) |
| | HR status | Positive | 3,074 (98.81) | 1,858 (98.51) | 1,216(99.27) | | Negative | 37 (1.19) | 28 (1.48) | 9 (0.73) |
| | HER2 status | Positive | 167 (5.37) | 114 (6.04) | 53 (4.33) | | Negative | 2,944 (94.63) | 1,772 (93.95) | 1,172 (95.67) |
| | Tumor subtype | Luminal A | 2,927 (94.09) | 1,761 (93.37) | 1,166 (95.18) | | Luminal B | 147 (4.73) | 97 (5.14) | 50 (4.08) | | TNBC | 17 (0.55) | 11 (0.58) | 6 (0.49) | | HER2 enrich | 20 (0.64) | 17 (0.90) | 3 (0.24) |
| | Regional LNM | Yes | 240 (7.71) | 152 (8.06) | 88 (7.18) | | No | 2,871 (92.29) | 1,734 (91.94) | 1,137 (92.82) |
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Notes: ※Others: defined as the Asian/Pacific Islander and American Indian/Alaska Native; ¶central: central portion of breast combined with nipple; ＆grade I: well differentiated, grade II: moderately differentiated, and grade III: poor differentiated; ￥stage: derived from the AJCC 7th guideline. Cervical LNM: central and lateral lymph node metastasis; HR: hormone receptor; TNBC: triple-negative breast cancer; HER2: human epidermal growth factor receptor-2.
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