Table I.

Patient characteristics.

Characteristic	Group	HER2-low (n=902)	HER2-negative (n=122)	P-value
Median age, years (range)		56.0 (20–93)	54.0 (23–90)	0.286
Median tumor size, cm		2.0	1.9	0.546
cT stage, n (%)	1	482 (53.4)	66 (54.1)	0.955
	2	357 (39.6)	46 (37.7)
	3	20 (2.2)	5 (4.1)
	4	43 (4.8)	5 (4.1)
Lymph node metastasis, n (%)	Yes	134 (14.9)	21 (17.2)	0.468
	No	768 (85.1)	101 (82.8)
Nuclear grade, n (%)	1	571 (63.3)	71 (58.2)	0.097
	2	141 (15.6)	20 (16.4)
	3	126 (14.0)	25 (20.5)
	Unknown	64 (7.1)	6 (4.9)
Estrogen receptor, n (%)	Positive	804 (89.0)	99 (82.0)	0.021
Progesterone receptor, n (%)	Positive	723 (80.2)	86 (71.3)	0.023
Median Ki67 (%)		14.5	18.5	0.013
Neoadjuvant chemotherapy, n (%)	Yes	168 (18.6)	29 (23.8)	0.160
	No	735 (81.5)	92 (75.4)
Adjuvant therapy, n (%)	Chemotherapy	141 (15.6)	19 (15.6)	0.894
	Endocrine	815 (90.4)	102 (83.6)	0.056
	Radiation	681 (75.5)	100 (82.0)	0.088