Stains & molecular markers
HER2 (c-erbB2) breast


Topic Completed: 1 June 2017

Minor changes: 15 May 2020

Copyright: 2002-2020, PathologyOutlines.com, Inc.

PubMed Search: HER2 [title] breast

See also HER2 stomach-GE junction

Mirna B. Podoll, M.D.
Emily S. Reisenbichler, M.D.
Page views in 2019: 10,119
Page views in 2020 to date: 8,406
Cite this page: Podoll MB, Reisenbichler ES. HER2 (c-erbB2) breast. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/stainsbreasther2.html. Accessed July 10th, 2020.
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 (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
Terminology
  • Also called Human Epidermal growth factor Receptor 2, c-erbB2, neu, ERBB2, CD340
Clinical features
    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
  • Click here for 2018 focused update
  • HER2 testing must be performed on every primary invasive carcinoma and on a metastatic site (if stage IV)
Tissue handling
  • 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)
Interpretation
    Equivocal Results
  • If initial HER2 testing by immunohistochemistry results in equivocal value, 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

    Heterogeneity
  • 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)

    Indeterminate Results
  • 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
Diagrams / tables

Images hosted on other servers:

HER2 IHC testing in breast carcinoma

HER2 single probe ISH in breast carcinoma

HER2 dual probe ISH in breast carcinoma

HER2/CEP17 ≥ 2.0, HER2 < 4 signals/cell

HER2/CEP17 < 2.0, HER2 copy number ≥ 6.0 signals/cell

HER2/CEP17 < 2.0,
HER2 copy number
≥ 4.0 and < 6.0
signals/cell

Case reports
Microscopic (histologic) images

Contributed by
Emily S. Reisenbichler, M.D.

Missing Image

HER2 IHC: 1+, 2+, 3+


 Contributed by
 Semir Vranić, M.D., Ph.D.

Missing Image

3+: IHC

Immunohistochemistry
  • Positive:
    • IHC 3+ (strong positive): tumor displays complete, intense circumferential membranous staining in > 10% of tumor cells (*readily appreciated using a low power objective and observed within a homogenous and contiguous invasive cell population)
  • Equivocal:
    • IHC 2+: weak to moderate complete membrane staining observed in > 10% of invasive tumor cells
  • Negative:
    • IHC 1+: incomplete faint membrane staining and within > 10% of invasive tumor cells
    • IHC 0: no staining observed or incomplete faint / barely perceptible membrane staining within ≤ 10% of invasive tumor cells
Molecular / cytogenetics description
    In situ hybridization (ISH)
  • The Panel recommends that concomitant IHC review should become part of the interpretation of single probe ISH results and the Panel preferentially recommends the use of dual probe instead of single probe ISH assays
  • Positive:
    • 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
  • Additional workup required:
    • If a case has a HER2/CEP17 ratio ≥ 2.0 but the average HER2 signals/cell is < 4.0, a definitive diagnosis will be rendered based on additional workup
    • If a case has an average of ≥ 6.0 HER2 signals/cell with a HER2/CEP17 ratio of < 2.0, formerly diagnosed as ISH positive for HER2, a definitive diagnosis will be rendered based on additional workup
    • If the case has an average HER2 signals/tumor cell of ≥ 4.0 and < 6.0 HER2 signals/cell and HER2/CEP17 ratio is < 2.0, formerly diagnosed as ISH equivocal for HER2, a definitive diagnosis will be rendered based on additional workup
  • Additional workup steps:
    • IHC testing for HER2 should be performed using sections from the same tissue sample used for ISH
      1. If the IHC result is 3+, diagnosis is HER2 positive
      2. If the IHC result is 2+, recount ISH by having an additional observer, blinded to previous ISH results, count at least 20 cells that include the area of invasion with IHC 2+ staining:
        • If reviewing the count by the additional observer changes the result into another ISH category, the result should be adjudicated per internal procedures to define the final category
        • If the count remains an average of < 4.0 HER2 signals/cell and HER2/CEP17 ratio is ≥ 2.0, the diagnosis is HER2 negative with a comment
        • If the HER2/CEP17 ratio remains < 2.0 with ≥ 6.0 HER2 signals/cell, the diagnosis is HER2 positive
        • If the count remains an average of ≥ 4.0 and < 6.0 HER2 signals/cell with HER2/CEP17 ratio < 2.0, the diagnosis is HER2 negative with a comment
      3. If the IHC result is 0/1+, diagnosis is HER2 negative with comment
  • Negative:
    • 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

    Contributed by Emily S. Reisenbichler, M.D.

    FISH images



    Images hosted on other servers:

    IHC and FISH

    Missing Image Missing Image

    CISH amplification: clusters and single signals


    Board review style 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 IHC was performed with equivocal (2+) result on the core biopsy of the breast. What is the next step in management?

    1. Report the result as equivocal and begin treatment
    2. Report the result as negative
    3. Repeat HER2 IHC on the breast core
    4. Perform HER2 FISH on the breast core
    5. Report the result as positive
    Board review answer #1
    D. The ASCO / CAP guidelines recommendations if initial HER2 testing by immunohistochemistry results in equivocal values, reflex testing by FISH should be performed on the same specimen or an alternative specimen (in this case the lymph node).

    Comment Here

    Reference: HER2 (c-erbB2) breast
    Back to top