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Breast malignant, males, children

Breast cancer

HER2 (c-erbB2)

Reviewer: Monika Roychowdhury, M.D. (see Reviewers page)
Revised: 7 May 2013, last major update February 2012
Copyright: (c) 2001-2013, PathologyOutlines.com, Inc.

General
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● HER2 gene encodes transmembrane growth factor receptor (p185)
● Cytoplasmic tyrosine kinase is constitutively active when overexpressed due to homo/heterodimerization (diagram)
● “3+” protein staining is associated with HER2 gene amplification at 17q21
● 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)

Terminology
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● Also called Human Epidermal growth factor Receptor 2, c-erbB2, neu, ERBB2, CD340

HER2 gene amplification
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● Present in 18-25% of breast tumors
● Associated with comedocarcinoma and aggressive invasive tumors
● Detectable by FISH; defined as increased ratio of HER2 gene to chromosome 17 (count > 2.2)
● Weak/moderate immunohistochemical staining is common without gene amplification
● Usually appears first in ADH or DCIS (Mod Pathol 2002;15:116)
● Also seen in nonbreast 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 Aug 8;7:153)

Detection of HER2 gene amplification
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● Predominantly determined using immunohistochemistry/IHC as screening test
● 3+ staining (see below) is highly correlated with gene amplification (FISH is more sensitive but more expensive, and it is difficult to distinguish in situ from invasive lesions because a fluorescent microscope must be used, which makes it difficult to assess histologic features (Mod Pathol 2000;13:1238, Hum Pathol 2005;36:250 [quality assurance])
● Can also detect with chromogenic in situ hybridization (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 in situ hybridization (SISH, Am J Clin Pathol 2009;132:514)
● CISH is comparable to FISH using ASCO/CAP criteria (Am J Clin Pathol 2009;131:490), even in cases with polysomy 17 and equivocal HercepTest results (Am J Clin Pathol 2009;132:228)
● CISH and SISH use a peroxidase enzyme labeled probe with chromogenic detection, allowing results to be visualized with standard bright-field 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)
● Can also use quantitative reverse transcription-polymerase chain reaction (Am J Clin Pathol 2008;129:563)
● FISH may be an appropriate screening test (instead of immunohistochemistry) under some conditions (Oncol Rep 2008;19:1271)
● Use of FISH cutpoint of 1.5 instead of 2.2 (signifies intermediate outcome between amplification negative and positive) has been suggested (Breast Cancer Res Treat 2008;112:453)
● For IHC, should compare intensity of patient sample to 3+ control slide with negative normal epithelium
● For node negative patients, FISH and IHC results are generally similar with some discrepant cases (Arch Pathol Lab Med 2001;125:746)
● Equivocal IHC and borderline FISH cases are difficult to interpret, even for highly experienced and validated laboratories (Mod Pathol 2007;20:584)
● External quality assurance is important (Am J Clin Pathol 2009;131:106)
● HER2 overexpression by IHC is associated with high Ki-67 index and negative ER/PR
● Note: even low level HER2 expression, without amplification, may be an adverse prognostic factor (Am J Surg Pathol 2009;33:759)

ASCO/CAP recommendations
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(a) Determine HER2 by IHC for all invasive breast cancer cases
(b) Specific procedures are recommended to reduce assay variation
(c) Define HER2 amplification as either 3+ IHC staining (uniform, intense stain of >30% of tumor cells), FISH of > 6 HER2 gene copies/nucleus or FISH ration > 2.2
(d) Define negative tests as 0 or 1+ IHC, FISH <4.0 or FISH ratio < 1.8
(e) Classify other results as equivocal, and perform additional testing
(f) Labs should show 95% concordance with another validated test (Arch Pathol Lab Med 2007;131:18, Mod Pathol 2008;21 Suppl 2:S8); similar recommendations in UK (J Clin Pathol 2008;61:818)

● FDA and ASCO/CAP schemes for HER2 evaluation select patients differently, with major discordances for low-grade, borderline HER2 amplification (Am J Clin Pathol 2008;129:907); high concordance between FISH and ISH requires modification of FDA scoring system (Mod Pathol 2008;21:1271)
● Standardized formalin fixation (minimum of 6 hours for core biopsies) is also important for IHC / FISH concordance (Arch Pathol Lab Med 2009;133:775), as is not delaying formalin fixation by more than one hour (Mod Pathol 2009;22:1457)
● Guidelines for evaluating genetic heterogeneity in HER2 testing have been produced (Arch Pathol Lab Med 2009;133:611)

Staining pattern
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● 0 (negative) - no staining or membrane staining in <30% of tumor cells
● 1+ (negative) - faint membrane staining in > 30% of tumor cells; only part of membrane is stained
● 2+ (weak positive) - weak/moderate complete membrane staining in >30% of tumor cells
● 3+ (strong positive) - strong complete membrane staining in >30% of tumor cells
● Note: 30% threshold is from ASCO/CAP scheme in 2008, prior threshold was 10%
● IHC stain scores of 0/1+ (negative/weak) or 3+ (strong) are predictive of FISH results (negative and positive amplification respectively)
● 2+ is not predictive and has significant interobserver variability (Mod Pathol 2001;14:1079)
● Suggested to perform FISH or PCR for 2+ tests (Am J Clin Pathol 2005;123:766)
● For equivocal HER2 results by FISH or PCR on breast core biopsies, recommended to evaluate on larger tumor sample (Am J Clin Pathol 2008;129:383)
● Normalization of IHC markedly improves concordance between IHC and FISH (Mod Pathol 2008;21:1271)
● Serum HER2 levels may predict histopathologic response to chemotherapy (Am J Clin Pathol 2007;128:630), and presence of HER2 mRNA-positive circulating tumor cells is independent prognostic factor in women with early breast cancer (Breast Cancer Res Treat 2009;117:525)
● HER2 gene status remains highly conserved as breast cancers metastasize; the discrepancies present are often due to interpretational difficulties and heterogeneity of HER2 amplification (Breast Cancer Res 2007;9:R31)

Testing algorithm
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HER2/neu testing algorithm

Case reports
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● Overgrowth of HER2 negative cells after anti-HER2 antibody therapy (Hum Pathol 2004;35:379)

Micro images
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Immunohistochemistry:

3+: IHC

3+: IHC, CISH and FISH

2+: IHC

1+: IHC

Various images:

Strong versus weak staining

Heterogeneous staining

FISH, CISH:

FISH amplification

IHC and FISH

FISH: amplified and not amplified

Not amplified - CISH and FISH


CISH amplification: clusters and single signals

CISH - not amplified, amplified, borderline amplification, equivocal signals

CISH and IHC

Various images

DCIS with ER and HER2 double immunostaining

Ductal hyperplasia, ADH, DCIS, and invasive carcinoma

Videos
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HER2 Testing

Additional references
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● Wikipedia, eMedicine

End of Breast malignant, males, children > Breast cancer > HER2 (c-erbB2)

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