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Breast malignant, males, children

Breast cancer

HER2 (c-erbB2)


Reviewer: Monika Roychowdhury, M.D. (see Reviewers page)
Revised: 7 October 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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● Click here for 2013 update
(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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