Characterization and clinical evaluation of microsatellite instability and loss of heterozygosity in tumor-related genes in gastric cancer

Analysis of biopsies of gastric cancer, intestinal and diffuse, and non-atrophic gastritis: an overview of loss of heterozygosity in Mexican patients

This study analyzed the loss of heterozygosity (LOH) effect on gastric cancer (GC) tumor samples from 21 Mexican patients, including diffuse (DGC) and intestinal (IGC) subtypes, as well as non-atrophic gastritis (NAG, control). Whole-genome high-density arrays were performed, and LOH regions were identified among the tissue samples. The differences in affected chromosomes were established among groups, with chromosomes 6 and 8 primarily affected in DGC and chromosomes 3, 16, and 17 in IGC. Functional pathway analysis revealed involvement in cancer-associated processes, such as signal transduction, immune response, and cellular metabolism. Five LOH-genes (IRAK1, IKBKG, PAK3, TKTL1, PRPS1) shared between GC and NAG suggest an early role in carcinogenesis. Specific genes were highlighted for Hallmarks of Cancer NAG-related genes (PTPRJ and NDUFS) were linked to cell proliferation and growth; IGC genes (GNAI2, RHOA, MAPKAPK3, MST1R) to genomic instability, metastasis, and arrest of cell death; and DGC genes to energy metabolism and immune evasion. These findings emphasize the role of LOH in GC pathogenesis and underscore the need for further research to understand LOH-affected genes and their diagnostic or evolution potential in cancer management. Portions of this text were previously published as part of a preprint (https://www.medrxiv.org/content/10.1101/2024.07.29.24311063v1).

Low incidence of microsatellite instability in gastric cancers and its association with the clinicopathological characteristics: a comparative study

Gastric cancer is a complex heterogeneous disease with different molecular subtypes that have clinical implications. It is characterized by high mortality rates and limited effective therapies. Microsatellite instability (MSI) has been recognized as a subgroup with a good prognosis based on TCGA and ACRG categorizations. Besides its prognostic and predictive value, gastric cancers with high MSI exhibit different clinical behaviors. The prevalence of high MSI has been assessed in gastric cancer worldwide, especially in East Asia, but there is a lack of such information in the Middle East. Therefore, this study aimed to investigate the incidence and status of MSI in Iranian gastric cancer patients using 53 samples collected from 2015 to 2020 at Taleghani Hospital Medical Center. DNA from tumoral and normal tissues were extracted and assessed through multiplex-PCR based on five mononucleotide repeats panel. Clinicopathological variables, including age, sex, Lauren classification, lymph node involvement, TNM stage, differentiation, localization, and tumor size, were also analyzed. With 2 males and 2 females, high microsatellite instability represented a small subgroup of almost 7.5% of the samples with a median age of 60.5 years. High microsatellite instability phenotypes were significantly associated with patients aged 68 years and older (p‑value of 0.0015) and lower lymph node involvement (p‑value of 0.0004). Microsatellite instability was also more frequent in females, with distal gastric location, bigger tumor size, and in the intestinal type of gastric cancer rather than the diffuse type.

Concordance between microsatellite instability testing and immunohistochemistry for mismatch repair proteins and efficient screening of mismatch repair deficient gastric cancer

Microsatellite instability (MSI) testing, an established technique that has gained prominence in recent years for its predictive potential regarding the efficacy of immune checkpoint inhibitors, is used to evaluate DNA mismatch repair (MMR) deficiency (dMMR). As with other methods, the immunohistochemistry (IHC) of MMR proteins is also widely adopted. Although both techniques have been validated, their concordance rate remains unknown, particularly regarding non-colorectal cancer. Therefore, the aim of the present study was to explore and elucidate their concordance in the context of gastric cancer (GC). A total of 489 surgically resected primary GC tissues were analyzed to compare the results yielded by the MSI test and those from IHC. Of 488 GC cases, 56 (11.5%) exhibited a loss of MMR proteins, whereas 52 (10.7%) were classified as high-frequency MSI (MSI-H). The concordance rate between these two categories was 99.2%. The microsatellite markers BAT26 and MONO27 demonstrated 100% sensitivity and 99.5% specificity in detecting dMMR GC. In addition, histopathological analysis revealed that MSI-H was more prevalent in GCs exhibiting coexisting Tub2 and Por1 subtypes. However, four discordant cases were observed. All four cases were microsatellite-stable cases but exhibited loss of MLH1 protein expression with hypermethylation of the MLH1 promoter. The results of the present study highlight that while there is a strong concordance between MSI and IHC testing results for determining dMMR status, IHC testing may offer superior efficacy in detecting dMMR.