HER2 (Human Epidermal growth Factor Receptor 2), which is also known as c-erb2, net, ERBB2, and CD340 is a member of the human epidermal growth factor receptor family (HER1, HER2, HER3, and HER4). Interestingly HER1 is also known as EGFR (epidermal growth factor receptor).
HER2 is clinically significant, in that a subset of breast carcinomas (<20%) show over expression of HER2 protein. A subset of HER2 positive tumors will respond to Herceptin® (Trastuzumab), which is a monoclonal antibody inhibitor (especially effective in the neoadjuvant treatment setting). There are two methods to detect HER2 over expression: immunohistochemistry (IHC) and in situ hybridization (FISH or CISH). ISH and IHC are generally considered equivalent, but cases not positive by IHC, which do not meet fixation criteria or have 2+ (equivocal) expression, should be submitted for additional ISH analysis.
HER2 IHC Interpretation
HER2 IHC expression is membraneous, and is classified as negative (0 or 1+), equivocal (2+), or positive (3+). The following are the interpretive criteria based on the 2013 CAP/ASCO guidelines:
Comment
0
No staining or faint barely perceptible staining in <10% of invasive tumor cells.
1+
Faint / incomplete barely perceptible membrane staining in >10% of invasive tumor cells.
2+
Circumferential membrane staining weak / moderate and/or incomplete in >10% of invasive tumors cells. Strong complete membraneous staining in <10% of invasive tumor cells.
3+
Strong complete membrane staining in >10% of the invasive tumor cells.
Cytoplasmic Staining
One of the most common causes of false positive interpretation is due to cytoplasmic staining. There are multiple potential causes of this pattern of staining, including technical and pathobiological. Small studies have found a significant proportion of cases with cytoplasmic expression to have neuroendocrine differentiation.
Important Points
CAP-ASCO recommendations are for <1 hr. from time of excision/biopsy to having a cut edge of tumor in 10% neutral buffered fomalin fixative (necrosis time). Fixation window is now 6-72 hrs (time extended from 48 to 72 hours in the updated 2013 guidelines). Over-fixation is probably not a clinically significant issue practically, but given the absence of relevant IHC data and the highly regulated environment surrounding HER2 testing, f/u FISH testing for negative results (outside the fixative window) is necessary.
Equivocal (2+) IHC results should be followed-up with FISH testing, if IHC is used as the initial testing modality (most common). Less than 1/3rd of equivocal cases show Her2 over-expression by FISH analysis.
Photomicrographs
Her-2 – Score = 0HER-2 – Score = 1+ (negative)HER-2 – Score = 3+Cytoplasmic staining with Her-2. Should consider excluding neuroendocrine differentiation. This case was scored by computer analysis as 3+, but FISH was negative (including the final interpretation).
References
Wolff, A. C., Hammond, M. E. H., Hicks, D. G., Dowsett, M., McShane, L. M., Allison, K. H., et al. (2013). Recommendations for Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer: American Society of Clinical Oncology/College of American Pathologists Clinical Practice Guideline Update. Archives of pathology & laboratory medicine. doi:10.5858/arpa.2013-0953-SA
Tafe, L. J., Janjigian, Y. Y., Zaidinski, M., Hedvat, C. V., Hameed, M. R., Tang, L. H., et al. (2011). Human epidermal growth factor receptor 2 testing in gastroesophageal cancer: correlation between immunohistochemistry and fluorescence in situ hybridization. Archives of pathology & laboratory medicine, 135(11), 1460–1465. doi:10.5858/arpa.2010-0541-OA
Arafah M, Kfoury HK, Zaidi SN. HER2/neu Immunostaining in Invasive Breast Cancer: Analysis of False Positive Factors. Oman Med J. 2010;25: 261–263. doi:10.5001/omj.2010.78
Horiguchi S-I, Hishima T, Hayashi Y, Shiozawa Y, Horiguchi K, Kuroi K, et al. HER-2/neu cytoplasmic staining is correlated with neuroendocrine differentiation in breast carcinoma. J Med Dent Sci. 2010;57: 155–163.
