In this issueImmunohistochemistry as a surrogate for molecular subtyping of gastric adenocarcinoma☆,☆☆
Introduction
Several classification schemes exist for gastric adenocarcinoma [1]. One of the most enduring, the Laurén classification, divides tumors into intestinal type and diffuse type based primarily on microscopic appearance [2]. The World Health Organization expands on morphologic subtypes, including varieties such as papillary, tubular, and mucinous adenocarcinoma [3]. Other classifications group tumors based on clinical stage (early versus advanced disease) and gross configuration (polypoid, fungating, ulcerated, and infiltrative) [3].
The Research Network of The Cancer Genome Atlas (TCGA) recently categorized gastric adenocarcinoma into 4 subtypes via molecular analysis: Epstein-Barr virus (EBV)–positive tumors, microsatellite-unstable tumors with MLH1 hypermethylation, genomically stable tumors, and tumors with chromosomal instability (CIN), of which 71% harbor TP53 mutation [4]. Although similar molecular alterations have been described in isolation, TCGA proposed a streamlined, stepwise process for characterizing a gastric carcinoma based on its predominant molecular profile, which may have clinical relevance based on subtype prognosis and targeted therapy options.
Given that alterations in MLH1 and TP53 and infection with EBV were prominent findings in TCGA's classification scheme, we hypothesized that immunohistochemical (IHC) staining and in situ hybridization of tissue samples from gastric adenocarcinomas could approximate the scheme in a simple and cost-effective manner. Furthermore, given that treatment of gastric carcinoma is influenced by amplification of the ERBB2 gene (which encodes the HER2 protein) [5], we set out to determine the relationship, if any, between HER2 overexpression and TCGA's defined molecular subtypes.
Section snippets
Materials and methods
With appropriate Research Subjects Review Board approval, we identified 104 cases of gastric adenocarcinoma in our departmental archives with available clinicopathological patient data, hematoxylin and eosin–stained slides, and tissue blocks. This included HER2 data (evaluated by IHC and/or fluorescence in situ hybridization [FISH]). We performed IHC staining for MLH1 (clone G168-15, dilution 1:50; Biocare Medical, Concord CA) and p53 (clone DO-7, ready to use; Dako North America, Carpinteria,
Results
The 104 cases, each from a different patient, included 46 biopsies and 58 resections. Staining results categorized the cases as follows: group 1 (EBER positive), 7 cases (7%); group 2 (MLH1 deficient), 17 cases (16%); group 3 (strong p53 staining, EBER negative, retained MLH1), 40 cases (38%); and group 4 (unremarkable staining pattern), 40 cases (38%). EBER positivity and MLH1 loss were mutually exclusive; strong p53 staining was seen in 3 EBER-positive and 5 MLH1-deficient cases.
Relevant
Discussion
Before TCGA's work in classifying gastric adenocarcinomas based on molecular genotype, several research groups had investigated the genetic characteristics of stomach cancer, with findings complementary to those of TCGA.
Infection with EBV has been linked to the development of many types of malignancy, including 5%-25% of gastric carcinomas [10]. This association is particularly strong with the subtype known as lymphoepithelioma-like carcinoma [11]. It has also been linked to several
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2022, Computational and Structural Biotechnology JournalCitation Excerpt :A solution with limited potential is immunohistochemistry combined with in situ hybridization with the following markers proposed for performing the subclassification: Epstein-Barr positive, p53 and MMR proteins [43,53]. This technique is a surrogate for the molecular subtyping, offering an efficient and reasonably accurate alternative, although separating GS from CIN is difficult, this has potential prognostic and therapeutic implications [54]. Furthermore, in 2018, Birkman et al. [53] used immunohistochemistry and in situ hybridization to achieve biologically and clinically relevant subgroups of GAC based on the histological Laurén classification of tumors.
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Competing interests: The authors all declare that they have no conflict of interest regarding this manuscript.
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Funding/Support: This project was supported by grant 1 UL1 RR024160-01 from the National Center for Research Resources (NCRR) (Bethesda, MD), a component of the National Institutes of Health (NIH) (Bethesda, MD) and the NIH Roadmap for Medical Research, and its contents are solely the responsibility of the authors and do not necessarily represent the official view of NCRR or NIH. Information on NCRR is available at http://www.ncrr.nih.gov. Information on Re-engineering the Clinical Research Enterprise can be obtained from http://nihroadmap.nih.gov/clinicalresearch/overview-translational.asp.
Dr Whitney-Miller receives grant funding from Genentech (South San Francisco, CA), a portion of which was used to perform HER2 testing on the cases in the studied cohort.