Table 2.

Baseline characteristics and association between dichotomized serum HER2 ECD level and clinicopathologic variables

Characteristics	Total group		Subgroup with normal serum HER2 ECD level (≤15.2 ng/ml)		Subgroup with elevated serum HER2 ECD level (>15.2 ng/ml)		P a
	n	%	n	%	n	%
Total patients	2,862	100%	2,736	100%	126	100%
Serum HER2 ECD, ng/ml
Mean ± SD	10.1 ± 9.4		9.3 ± 1.9		27.3 ± 40.4		<0.001b
Median (range)	9.2 (3.3–427.8)		9.1 (3.3–15.2)		18.5 (15.3–427.8)
Age at diagnosis, years							0.860b
Mean ± SD	48.5 ± 9.9		48.5 ± 9.9		48.4 ± 10.3
Median (range)	48 (22–94)		48.0 (22–94)		49.0 (26–88)
Age subgroup, years
≤ 34	172	6%	162	6%	10	8%	0.100
35–49	1,510	53%	1,455	53%	55	44%
≥ 50	1,180	41%	1,119	41%	61	48%
Stage
I/II	2,457	86%	2,376	87%	81	64%	<0.001
III	405	14%	360	13%	45	36%
Tumor size, cm
≤ 2	1,676	59%	1,625	59%	51	40%	<0.001
> 2	1,186	41%	1,111	41%	75	60%
Lymph node
Negative	1,749	61%	1,694	62%	55	44%	<0.001
Positive	1,113	39%	1,042	38%	71	56%
Histologic grade
1/2	1,787	64%	1,734	65%	53	43%	<0.001
3	1,025	36%	954	35%	71	57%
Unknown	50		48		2
Nuclear grade
1/2	1,775	63%	1,730	64%	45	41%	<0.001
3	1,049	37%	984	36%	65	59%
Unknown	38		22		16
LVI
Negative	2,095	76%	2,007	76%	88	75%	0.830
Positive	660	24%	631	24%	29	25%
Unknown	107		98		9
Hormone-receptor status
Negative	916	32%	831	30%	85	68%	<0.001
Positivec	1,940	68%	1,899	70%	41	32%
Unknown	6		6		0
Tissue HER2 status
Negative	2,168	76%	2,146	79%	22	17%	<0.001
Positived	692	24%	588	21%	104	83%
Unknown	2		2		0
Definitive surgery							<0.001
Conservation	1,781	62%	1,743	64%	38	30%
Mastectomy	1,081	38%	993	36%	88	70%
Radiotherapy
Yes	2,047	72%	1,973	72%	74	59%	0.001
No	813	28%	761	28%	52	41%
Unknown	2		2		0
Chemotherapy
Yes	1,852	65%	1,746	64%	106	84%	<0.001
No	1,007	35%	987	36%	20	16%
Unknown	3		3		0
Anti-HER2 therapy
Yes	264	9%	211	8%	53	42%	<0.001
No	2,598	91%	2,525	92%	73	58%

^aCalculated by chi-square test except where stated otherwise.

^bCalculated by t-test.

^cEstrogen- and/or progesterone-receptor positive.

^dGraded as 3+ on IHC or 2+ on fluorescence in situ hybridization in cases of IHC 2+.