HER2 immunohistochemistry in invasive micropapillary breast carcinoma: Complete assessment of an incomplete pattern Journal Article
| Authors: | Perron, M.; Wen, H. Y.; Hanna, M. G.; Brogi, E.; Ross, D. S. |
| Article Title: | HER2 immunohistochemistry in invasive micropapillary breast carcinoma: Complete assessment of an incomplete pattern |
| Abstract: | Context.-Invasive micropapillary carcinoma (IMPC) is a rare variant of breast carcinoma, composed of avascular morula-like tumor clusters surrounded by stromal spaces, which can affect the HER2 immunohistochemical (IHC) staining pattern. The 2013 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) HER2 testing guideline suggests moderate to intense but incomplete (basolateral) staining be considered equivocal. Objectives.-To perform a detailed assessment of HER2 IHC staining patterns in IMPC. Design.-Hematoxylin-eosin and HER2 IHC slides were retrospectively reviewed to assess the morphology and HER2 IHC characteristics of IMPC. The 2018 ASCO/CAP guideline was applied. Results.-The cohort consisted of 187 IMPCs from 181 patients with median age of 58 years. Homogeneous (≥90%) micropapillary component was found in 40% (75 of 187) of cases. Receptor profile was as follows: 75% (140 of 187) ERþ HER2-, 19% (37 of 187) ERþ HER2þ, 4% (7 of 187) ER- HER2þ, and 2% (3 of 187) ER- HER2-. Of 26 cases with HER2 IHC 3þ, 65% (17 of 26) showed a basolateral staining pattern with strong intensity. HER2 fluorescence in situ hybridization (FISH) showed amplification in 26% (17 of 66) of HER2 IHC equivocal cases: 76% (13 of 17) showed basolateral staining pattern and 24% (4 of 17) complete staining, with weak to moderate (2), moderate (14), or moderate to strong (1) intensity. Conclusions.-The most frequent staining pattern was basolateral, seen in 49% of cases, including 65% HER2 IHC positive and 76% HER2 IHC equivocal/FISH amplified. If a basolateral pattern and weak to moderate staining is observed in IMPC, alternative testing should be performed to confirm the HER2 status. © 2021 College of American Pathologists. All rights reserved. |
| Journal Title: | Archives of Pathology & Laboratory Medicine |
| Volume: | 145 |
| Issue: | 8 |
| ISSN: | 0003-9985 |
| Publisher: | College of American Pathologists |
| Date Published: | 2021-08-01 |
| Start Page: | 979 |
| End Page: | 987 |
| Language: | English |
| DOI: | 10.5858/arpa.2020-0288-oa |
| PUBMED: | 33212478 |
| PROVIDER: | scopus |
| PMCID: | PMC9382909 |
| DOI/URL: | |
| Notes: | Review -- Export Date: 1 September 2021 -- Source: Scopus |
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