Table of ContentsDefinition / general | Terminology | Clinical features | Tissue handling | Interpretation | Diagrams / tables | Case reports | Microscopic (histologic) images | Immunohistochemistry | Molecular / cytogenetics description | Molecular / cytogenetics images | Board review question #1 | Board review answer #1 | Additional references
Cite this page: Podoll M. HER2 (c-erbB2) breast. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/stainsbreasther2.html. Accessed May 27th, 2019.
Definition / general
- HER2/neu is the human epidermal growth factor receptor 2, also called ERBB2 (Erb-B2 receptor tyrosine kinase 2)
- HER2 gene encodes transmembrane growth factor receptor (p185)
- Cytoplasmic tyrosine kinase is constitutively active when overexpressed due to homo / heterodimerization (BioMed Central - The role of Herceptin in early breast cancer; International Seminars in Surgical Oncology 2008; 5:9)
- The biologic impact of HER2 gene amplification is not due to (a) mere chromosome 17 polysomy without HER2 gene amplification (Am J Surg Pathol 2005;29:1221) or (b) chromosome 17 aneusomy
- Aneusomy means other than 2 copies of chromosome (Mod Pathol 2002;15:137)
- Also called Human Epidermal growth factor Receptor 2, c-erbB2, neu, ERBB2, CD340
HER2 gene amplification / protein overexpression
- Present in approximately 15 - 20% of breast tumors
- Associated with comedocarcinoma and aggressive invasive tumors
- Usually appears first in ADH or DCIS (Mod Pathol 2002;15:116)
- Also seen in non breast cancers (Mod Pathol 2007;20:192)
- Anti-HER2 therapy (trastuzumab / Herceptin®) plus chemotherapy reduces recurrence, metastases and mortality in HER2 gene amplified breast cancer patients (Int Semin Surg Oncol 2008;5:9, Acta Oncol 2008;47:1564); Lapatinib (Tykerb®) has a similar effect (Biologics 2009;3:289)
- Anti-HER2 therapy may improve survival in metastatic disease (Am J Clin Oncol 2008;31:250, N Engl J Med 2007;357:1496) but is associated with cardiac toxicity (BMC Cancer 2007;7:153)
- To detect, the most commonly used in situ hybridization (ISH) is a dual probe fluorescent ISH (FISH) using fluorochrome labeled probes for (a) the HER2 locus on the long arm of chromosome 17 and (b) a site near the centromere of chromosome 17 (CEN17 or CEP17)
- In situ hybridization detects HER2 gene amplification as evaluated by counting at least 20 tumor cells and estimating the HER2 copy number and the HER2/CEP17 ratio
- Amplification can also be detected with chromogenic ISH (CISH), (Mod Pathol 2002;15:657, Mod Pathol 2005;18:1015, Mod Pathol 2006;19:481, Breast Cancer Res 2007;9:R68) and silver enhanced ISH (SISH) (Am J Clin Pathol 2009;132:514)
- CISH and SISH use a peroxidase enzyme labeled probe with chromogenic detection, allowing results to be visualized with standard brightfield microscopy, so histologic features and HER2 status can be evaluated in parallel; signals do not decay over time, unlike FISH (Am J Clin Pathol 2009;132:539)
- Chromogenic in situ hybridization (CISH) is the only FDA approved single probe ISH test for HER2
- Quantitative reverse transcription polymerase chain reaction can also be used (Am J Clin Pathol 2008;129:563)
- Immunohistochemistry (IHC) detects evidence of protein overexpression via evaluation of the membranous staining in the tumor cells
- Testing must be performed in accredited laboratories
ASCO / CAP recommendations for HER2 testing and result interpretation
- Click here for 2013 update
- HER2 testing must be performed on every primary invasive carcinoma and on a metastatic site (if stage IV)
- Cytology specimens, needle biopsies and resection specimens can be used for testing
- Cold ischemia time must be limited, with the time to fixative within 1 hour
- Tissue fixed in 10% neutral buffered formalin between 6 - 72 hours
- Testing must be performed according to standardized analytically validated protocols
- Labs should show 95% concordance with another validated test (Arch Pathol Lab Med 2007;131:18, Mod Pathol 2008;21:S8); similar recommendations in UK (J Clin Pathol 2008;61:818)
- If initial HER2 testing by either immunohistochemistry or FISH results in equivocal values, reflex testing should be performed on the same specimen using the alternative test OR perform testing on a new specimen, if available, using the same or alternative test
- Approximately 20 - 30% cases could be classified as heterogeneous
- The HER2/CEP17 ratio of each cohesive clone with amplification should be included in the report
- Cases in which > 10% of cells are amplified (in a minimum of 20 non overlapping cells in the amplified and non amplified areas) should be regarded as HER2+, while cases in which 1 - 10% tumor cells show amplification should be regarded as HER2 negative
- Tumors with scattered amplified cells should be categorized based on the overall score for the cells counted (minimum of 60 cells) (Mod Pathol 2014;27:4)
- HER2 may be reported as indeterminate if technical problems preclude the reporting of a positive, negative or equivocal test result
- Reasons include improper specimen handling, crush artifact, edge artifacts and analytical testing failures
- In these cases, the reasoning for an indeterminate result should be reported and additional tissue should be acquired for testing
- Overgrowth of HER2 negative cells after anti-HER2 antibody therapy (Hum Pathol 2004;35:379)
Microscopic (histologic) images
- IHC 3+ (strong positive): tumor displays complete, intense circumferential membranous staining
- IHC 2+: incomplete circumferential membrane staining or weak / moderate and within >10% of invasive tumor cells; or complete and circumferential membrane staining that is intense and within ≤10% of invasive tumor cells
- IHC 1+: incomplete faint membrane staining and within >10% of invasive tumor cells
- IHC 0: no staining observed or incomplete faint membrane staining within ≤10% of invasive tumor cells
Molecular / cytogenetics description
In situ hybridization (ISH)
- Single probe average HER2 copy number ≥ 6.0 signals/cell
- Dual probe HER2/CEP17 ratio ≥ 2.0 with any average HER2 copy number, or HER2/CEP17 < 2.0 with an average HER2 copy number ≥ 6.0 signals / cell
- Single probe ISH average HER2 copy number ≥ 4.0 and < 6.0 signals/cell
- Dual probe HER2/CEP17 ratio < 2.0 with an average HER2 copy number ≥ 4.0 and < 6.0 signals/cell
- Single probe average HER2 copy number < 4.0 signals / cell
- Dual probe HER2/CEP17 ratio < 2.0 with an average HER2 copy number < 4.0 signals/cell
Molecular / cytogenetics images
Board review question #1
- A woman with a right breast mass and axillary lymphadenopathy was found to have invasive mammary carcinoma with a positive lymph node. HER2 by FISH was performed with equivocal results on the core biopsy of the breast. What is the next step in management?
- Report the result as equivocal and begin treatment.
- Report the result as negative.
- Repeat HER2 FISH on the breast core.
- Perform HER2 by immunohistochemistry on the breast core.
- Report the result as amplified.
Board review answer #1
D. The ASCO / CAP guidelines recommendations if initial HER2 testing by either immunohistochemistry of FISH results in equivocal values, reflex testing should be performed on the same specimen or an alternative specimen (in this case the lymph node) using the alternative test. In this case, if the results of FISH of the breast core biopsy are equivocal, one could reflex to IHC on the same breast tissue, or perform testing on the involved lymph node.