Table 2.

HER2 status of primary tumors compared to HER2 status in macrometastases in ipsilateral lymph nodes.

Metastases in the ipsilateral lymph node Number of cases, n (%)
Primary tumor	Protein level	0/1+	2+	3+	Total
	0/1+	25 (92.6)	9 (33.3)	0 (0.0)	27a (62.8)
	2+	4 (57.1)	6 (85.7)	0 (0.0)	7b (16.3)
	3+	1 (11.1)	2 (22.2)	6 (66.7)	9 (20.9)
	43
	HER2/CEP17 ratio	<2		≥2
	<2	31 (96.9)		1 (3.1)	32 (76.2)
	≥2	2 (20.0)		10 (100)	10c (23.8)
					42d
	Average HER2 copy number (signals/cell)	<4.0		≥4.0
	<4.0	34 (100.0)		0 (0.0)	34 (81.0)
	≥4.0	3 (37.5)		5 (62.5)	8 (19.0)
					42d
	HER2 statuse	Negative		Positive
	Negative	34 (100)		0 (0.0)	34 (79.1)
	Positive	3 (33.3)		6 (66.7)	9 (20.9)
	43

a) Seven cases with HER2 0/1+ primary tumors displayed both macrometastases diagnosed as HER2 0/1+ and macrometastases diagnosed as HER2 2+.

b) Three cases with a primary tumor diagnosed as HER2 2+ showed both macrometastases diagnosed as HER2 0/1+ and macrometastases diagnosed as HER2 2+.

c) Two cases with a primary tumor showing a HER2/CEP17 ratio ≥2 displayed both macrometastases with a HER2/CEP17 ratio <2 and macrometastases with a HER2/CEP17 ratio ≥2.

d) One case including one primary tumor and two macrometastases was excluded from the analysis because the primary tumor was not genetically analyzed.

e) Based on HER2 protein level, HER2/CEP17 ratio, and average HER2 copy number, in accordance with the 2018 ASCO/CAP guidelines.