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Table 2 Interpretation guidelines for HER2 IHC and FISH changes in our case

From: Sterile, abscess-like cerebral lesion during trastuzumab therapy after HER2 status switch in a triple negative breast cancer patient: a case report and literature review

YEAR

LESION/MATERIAL EXAMINED

HER2 IHC

HER2 FISH

Respective ASCO/CAP GUIDELINE definition for HER2 positive IHC result

Respective ASCO/CAP GUIDELINE definition for HER2 positive ISH result

2010

Primary tumor

surgical resection specimen

20% of tumor cells showed complete, intense circumferential membrane reaction:

2+

(SP3 antibody)

Polysomy of Chr17 suggested: many tumor cells showed 3–6 HER2 copies/cell

Interpreted as HER2 negative

(single probe ISH assay)

2007 ASCO/CAP guideline

> 30% of tumor cells show complete, intense circumferential reaction

2007 ASCO/CAP guideline

> 6 HER2copy/cell (single probe ISH)

> 2.2 HER2/CEN17 ratio/cell (dual probe ISH)

2017

Metastasis (sternum region)

20% of tumor cells showed complete, weak or moderate, circumferential membrane reaction:

2+

(4B5 antibody)

30% of tumor cells showed polysomy-co-amplification

(3–6 CEP17 signals and 6–10 HER2 signals/cells; dual probe ISH assay)

Interpreted as HER2 positive

2013 ASCO/CAP guideline

> 10% of tumor cells show complete, in tense circumferential reaction

2013 ASCO/CAP guideline

See: Wolff AC et al. Arch Pathol Lab Med. 2014 Feb; 138 (2): 241–256.

2017

Metastasis

(brain – analysis following second opinion request)

15–20% of the tumor cells showed complete, weak or moderate, circumferential membrane reaction:

2+

(4B5 antibody)

80 tumor cells were counted: mean HER2 copy number/cell was 4.0, mean HER2/CEP17 ratio was 1.62. However,

scattered, heterogeneous amplification was present: In 43% of the tumor cells 4.6 HER2/cell was found and the HER2/CEP17 ratio was 2.4.

(dual probe ISH assay)

Interpreted as heterogeneous amplification, HER2 negative

2013 ASCO/CAP guideline

> 10% of tumor cells show complete, intense circumferential reaction

2013 ASCO/CAP guideline

and

2009 CAP guidelines for genetic heterogeneity in HER2 testing:

„HER2 genetic heterogeneity (GH) exists if there are more than 5% but less than 50% of infiltrating tumor cells with a ratio higher than 2.2 …. If more than 50% of the infiltrating tumor cells have a ratio higher than 2.2, then the tumor is considered HER2 amplified.”