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

Age, median (range), y^b

48 (20–94)

49 (21–92)

.127

48 (20–94)

49 (23–90)

.267

48 (20–91)

50 (21–91)

.001

Age, No, (%), y^b

.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)