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Table 1 Clinicopathological characteristics of patients with HER2-low breast cancer according to hormone receptor status

From: Clinical significance of HER2-low expression in early breast cancer: a nationwide study from the Korean Breast Cancer Society

Variables All patients (N = 30,491) P value HR-positive (N = 23,539)a P value HR-negative (N = 6,934) P value
HER2_0 HER2_L HER2_0 HER2_L HER2_0 HER2_L
Age, median (range), yb 48 (20–94) 49 (21–92) .127 48 (20–94) 49 (23–90) .267 48 (20–91) 50 (21–91) .001
Age, No, (%), yb    .267    .462    .410
 < 40 2,997 (14.2) 1,311 (13.8)   1,934 (12.4) 1,016 (12.9)   1,062 (19.9) 295 (18.5)  
 ≥ 40 17,985 (85.8) 81,76 (86.2)   13,682 (87.6) 68,77 (87.1)   4,268 (80.1) 1,297 (81.5)  
Sex, No. (%)    .021    .084    .547
 Female 20,909 (99.6) 9,454 (99.4)   15,557 (99.5) 7,860 (99.4)   5,336 (99.9) 1,592 (99.9)  
 Male 76 (0.4) 52 (0.6)   72 (0.5) 50 (0.6)   4 (0.1) 2 (0.1)  
Menopausal status, No. (%)b    .001    .001    .505
 Premenopause 7,474 (68.6) 4,373 (72.5)   5,541 (70.6) 3,628 (74.3)   1,928 (63.3) 739 (64.4)  
 Postmenopause 3,423 (31.4) 1,660 (27.5)   2,305 (29.4) 1,252 (25.7)   1,117 (36.7) 408 (35.6)  
BMI, No. (%), kg/m2    .001    .001    .015
 < 25 16,176 (77.1) 7,087 (74.6)   12,104 (77.4) 5,921 (74.8)   4,059 (76.0) 1,164 (73.0)  
 ≥ 25 4,809 (22.9) 2,419 (25.4)   3,525 (22.6) 1,989 (25.2)   1,281 (24.0) 430 (27.0)  
Presence of FHx, No. (%)b 1,394 (8.5) 739 (9.5) .010 1,003 (8.2) 612 (9.4) .005 391 (9.4) 127 (10.0) .500
Tumor location, No. (%)b    .447    .220    .546
 Right 9,752 (50.0) 4,066 (49.9)   7,393 (50.7) 3,403 (50.0)   2,354 (48.1) 670 (49.8)  
 Left 9,703 (49.8) 4,078 (50.0)   7,165 (49.1) 3,395 (49.9)   2,533 (51.7) 674 (50.1)  
 Both 43 (0.2) 9 (0.1)   26 (0.3) 7 (0.1)   8 (0.2) 2 (0.1)  
Pathological stage, No. (%)    .121    .334    .147
 Stage I 9,571 (45.6) 4,454 (46.9)   7,539 (48.3) 3,810 (48.2)   2,024 (37.9) 642 (40.3)  
 Stage II 8,860 (42.2) 3,935 (41.4)   6,180 (39.5) 3,181 (40.2)   2,673 (50.1) 754 (47.3)  
 Stage III 2,554 (12.2) 1,117 (11.7)   1,910 (12.2) 919 (11.6)   643 (12.0) 198 (12.4)  
pT stage, No. (%)c    .001    .041    .050
 T1 12,522 (59.8) 5,801 (61.1)   9,967 (63.9) 5,001 (63.3)   2,546 (47.8) 798 (50.2)  
 T2 7,594 (36.2) 3,365 (35.4)   5,078 (32.5) 2,631 (33.3)   2,510 (47.1) 734 (46.2)  
 T3 688 (3.3) 291 (3.1)   467 (3.0) 240 (3.0)   220 (4.2) 51 (3.2)  
 T4 146 (0.7) 35 (0.4)   97 (0.6) 28 (0.4)   49 (0.9) 7 (0.4)  
pN stage, No. (%)    .104    .213    .623
 N0 13,702 (65.3) 6,118 (64.4)   10,047 (64.3) 5,048 (63.8)   3,643 (68.2) 1,068 (67.0)  
 N1 4,978 (23.7) 2,376 (25.0)   3,856 (24.7) 2,034 (25.7)   1,119 (21.0) 342 (21.5)  
 N2 1,430 (6.8) 636 (6.7)   1,094 (7.0) 536 (6.8)   335 (6.3) 100 (6.3)  
 N3 875 (4.2) 376 (3.9)   632 (4.0) 292 (3.7)   243 (4.5) 84 (5.2)  
LNR, mean ± SD 0.085 ± 0.18 0.092 ± 0.20 .005 0.088 ± 0.18 0.092 ± 0.19 .104 0.077 ± 0.17 0.090 ± 0.20 .018
Histological type, No. (%)d    .007    .333    .059
 Invasive ductal 19,683 (96.4) 8,942 (95.8)   14,552 (95.5) 7,406 (95.3)   5,122 (99.1) 1,534 (98.6)  
 Invasive lobular 725 (3.6) 391 (4.2)   680 (4.5) 369 (4.7)   45 (0.9) 22 (1.4)  
Histological grade, No. (%)    .001    .001    .205
 G1 4,232 (20.2) 1,831 (19.3)   4,029 (25.8) 1,770 (22.4)   200 (3.7) 61 (3.8)  
 G2 8,430 (40.2) 4,437 (46.7)   7,341 (47.0) 4,081 (51.6)   1,087 (20.4) 355 (22.3)  
 G3 6,534 (31.1) 2,500 (26.3)   2,940 (18.8) 1,473 (18.6)   3,591 (67.2) 1,027 (64.4)  
 Unknown 1,789 (8.5) 738 (7.7)   1,319 (8.4) 586 (7.4)   462 (8.7) 151 (9.5)  
Nuclear grade, No. (%)    .001    .001    .783
 G1 2,483 (11.8) 849 (8.9)   2,342 (15.0) 806 (10.3)   141 (2.6) 43 (2.7)  
 G2 9,217 (44.0) 4,650 (48.9)   8,205 (52.5) 4,322 (54.6)   1,007 (18.9) 327 (20.5)  
 G3 6,380 (30.4) 2,523 (26.6)   2,968 (19.0) 1,568 (19.8)   3,410 (63.9) 954 (59.9)  
 Unknown 2,905 (13.8) 1,484 (15.6)   2,114 (13.5) 1,214 (15.3)   782 (14.6) 270 (16.9)  
Presence of LI, No. (%)b 5,231 (24.9) 2,712 (28.5) .001 3,913 (25.0) 2,284 (14.6) .001 1,316 (24.6) 428 (26.9) .001
Presence of VI, No. (%)b 2,737 (13.0) 1,171 (12.3) .148 2,048 (13.1) 960 (12.1) .338 689 (12.9) 211 (13.2) .202
Ki-67, No. (%)b          
 < 14% 4,962 (48.2) 3,035 (58.7) .001 4,415 (57.6) 2,793 (65.2) .001 539 (20.7) 242 (27.4) .001
 ≥ 14% 5,328 (51.8) 2,134 (41.3)   3,256 (42.4) 1,491 (34.8)   2,069 (79.3) 642 (72.6)  
 < 20% 5,752 (55.9) 3,390 (65.6) .001 5,115 (66.7) 3,095 (72.2) .001 629 (24.1) 295 (33.4) .001
 ≥ 20% 4,538 (44.1) 1,779 (34.4)   2,556 (33.3) 1,189 (27.8)   1,979 (75.9) 589 (66.6)  
Breast surgery, No. (%)b    .001    .004    .044
 BCS 12,972 (62.5) 5,656 (60.3)   9,603 (62.1) 4,698 (60.2)   3,363 (63.6) 958 (60.8)  
 TM 7,798 (37.5) 3,731 (39.7)   5,863 (37.9) 3,111 (39.8)   1,927 (36.4) 618 (39.2)  
Axillary surgery, No. (%)    .001    .001    .545
 SLNB 6,111 (29.1) 3,236 (34.0)   4,616 (29.6) 2,765 (35.0)   1,494 (28.0) 470 (29.5)  
 SLNB & ALND 4,177 (19.9) 2,366 (25.0)   3,196 (20.4) 2,023 (25.6)   980 (18.3) 343 (21.5)  
 ALND 9,353 (44.6) 3,465 (36.4)   6,790 (43.4) 2,751 (34.8)   2,559 (48.0) 714 (44.8)  
 No surgery 1,344 (6.4) 439 (4.6)   1,027 (6.6) 371 (4.7)   307 (5.7) 67 (4.2)  
Adjuvant RT, No. (%)b    .922    .747    .658
 Yes 13,220 (69.1) 5,882 (69.2)   9,773 (68.5) 4,856 (68.7)   3,444 (71.0) 1,026 (71.6)  
 No 5,907 (30.9) 2,621 (30.8)   4,497 (31.5) 2,212 (31.3)   1,407 (29.0) 407 (28.4)  
Adjuvant CT, No. (%)b    .002    .347    .141
 Yes 13,979 (71.3) 6,099 (69.4)   9,466 (64.9) 4,774 (65.5)   4,509 (89.9) 1,325 (88.6)  
 No 5,633 (28.7) 2,685 (30.6)   5,124 (35.1) 2,512 (34.5)   507 (10.1) 171 (11.4)  
  1. HR hormone receptor; HER2 human epidermal growth factor receptor 2; HER2_0 HER2-IHC 0 breast cancer; HER2_L HER2-low breast cancer; BMI body mass index; FHx family history; pT stage pathological T stage; pN stage pathological N stage; LNR lymph node ratio; SD standard deviation; LI lymphatic invasion; VI vascular invasion; BCS breast conserving surgery; TM total mastectomy; SLNB sentinel lymph node biopsy; ALND axillary lymph node dissection; RT radiotherapy; CT chemotherapy
  2. aHormone receptor status was available for a total of 30,473 patients: 23,539 in the hormone receptor-positive group, and 6934 in the hormone receptor-negative group
  3. bThese variables have missing data
  4. cThe cases of T0 are not described here
  5. dThe cases of other histology are not described here