. 2007 Jan;3(1):48–50. doi: 10.1200/JOP.0718501

Table 2.

HER2 Testing Results

	IHC HER2 Protein Expression	Testing Method
	IHC HER2 Protein Expression	FISH HER2 Gene Amplification
Positive	3+^*	HER2/CEP 17 ratio >2.2 or
		Average HER2 gene copy number >6^†
Equivocal	2+	HER2/CEP 17 ratio of 1.8-2.2 or
		Average HER2 gene copy number 4-6^†
Negative	0-1+	HER2/CEP 17 ratio <1.8 or
		Average HER2 gene copy number <4^†

NOTE. Definitions depend on laboratory documentation of the following elements: (1) proof of initial testing validation in which positive and negative HER2 categories are 95% concordant with alternative validated method or same validated method for HER2; (2) ongoing internal question-and-answer procedures; (3) participation in external proficiency testing; and (4) current accreditation by valid accrediting agency.

Abbreviations: IHC, immunohistochemistry; HER2, human epidermal growth factor receptor 2; FISH, fluorescence in situ hybridization; CEP 17, entromeric chromosome 17–specific probe.

* Defined as uniform intense membrane staining of >30% of invasive tumor cells.

† Signals/nucleus for those test systems without an internal central probe.