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

Intraoperative rapid immunohistochemistry of microsatellite instability using non-contact alternating current electric field mixing

OBJECTIVES

Tumors caused by failure of the DNA-mismatch repair system generally show microsatellite instability (MSI). High-frequency MSI cancers have been shown to be susceptible to immuno-oncology therapies. The aim of this study was to evaluate the clinical reliability of a rapid immunohistochemistry (IHC) technique for intraoperatively assessing molecular status through detection of tumoral deficiencies in the expression of mismatch repair proteins (dMMR; MLH1, MSH2, MSH6, and PMS2).

METHODS

The rapid IHC method uses non-contact alternating current (AC) mixing to achieve more rapid/stable staining within a minimum of 13 min during surgery. Sixteen formalin-fixed paraffin-embedded (FFPE) tumor samples from 3 dMMR patients with Lynch syndrome and 6 FFPE samples from 6 dMMR-cancer patients were collected to establish an IHC protocol for MMR proteins. Next, 26 surgical patients treated and whose MSI status was determined using PCR-based tests were retrospectively analyzed. The concordance of dMMR diagnoses for thoracic tumors between the conventional (frozen section (FS)- and FFPE-IHCs) and rapid AC-mixing IHC with FSs were compared.

RESULTS

A rapid IHC protocol using primary antibodies against four MMR proteins (mixed 5-10 min) was established (entire process within 40 min). The concordance rate for MMR-IHC between the conventional and rapid IHC was 100%. dMMR diagnoses including an MSI-high pulmonary sarcoma patient entirely matched between FS- and FFPE-IHC.

CONCLUSION

Rapid MMR-IHC could potentially serve as a clinical tool for intraoperative determination of tumor MSI/dMMR status. AC-mixing technology will contribute to improving pathological diagnostic capability through the development of an original and innovative rapid IHC.

Deep Gaussian process with uncertainty estimation for microsatellite instability and immunotherapy response prediction from histology

Determining tumor microsatellite status has significant clinical value because tumors that are microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) respond well to immune checkpoint inhibitors (ICIs) and oftentimes not to chemotherapeutics. We propose MSI-SEER, a deep Gaussian process-based Bayesian model that analyzes H&E whole-slide images in weakly-supervised-learning to predict microsatellite status in gastric and colorectal cancers. We performed extensive validation using multiple large datasets comprised of patients from diverse racial backgrounds. MSI-SEER achieved state-of-the-art performance with MSI prediction by integrating uncertainty prediction. We achieved high accuracy for predicting ICI responsiveness by combining tumor MSI status with stroma-to-tumor ratio. Finally, MSI-SEER's tile-level predictions revealed novel insights into the role of spatial distribution of MSI-H regions in the tumor microenvironment and ICI response.

Identification of genomic variants associated with colorectal cancer heredity in indigenous populations of the Amazon

Colorectal cancer (CRC) is a major global health concern, with genetic factors influencing its development. This study investigated the genomic profile of Amazonian indigenous populations (INDG) by analyzing five genes-APC, MLH1, MSH2, MSH6, and PMS2-associated with CRC. A total of 64 healthy individuals from 12 ethnic groups were analyzed using exome sequencing and bioinformatic tools. We identified 55 genetic variants, including three novel variants exclusive to the INDG, located in the MLH1 and MSH6 genes, which may represent genetic risks for CRC in this population. Additionally, three high-impact variants, already described in the literature, were identified in the APC and MSH2 genes. The study highlights the genetic isolation of Amazonian indigenous groups, with notable differences compared to continental populations. These findings emphasize the need for further genomic research to enhance the understanding of genetic risk factors and improve early detection and targeted therapies in vulnerable populations.

Mismatch repair deficiency and its relationship with histopathological features in gastric cancer patients

Gastric cancer is a common malignancy disease with a poor prognosis. Deficient mismatch repair is a prognostic and predictive marker of response to systemic therapies. However, deficient mismatch repair frequency and the relationship between this status and microscopic characteristics are inconsistent across nations. We aimed to determine the rate of deficient mismatch repair and its association with histopathological features in gastric cancer patients. A cross-sectional study was conducted on 226 gastric cancer patients treated at Hue University of Medicine and Pharmacy Hospital and Hue Central Hospital from June 2020 to January 2024. Mismatch repair protein expression was evaluated using immunohistochemical staining, and any absence of mismatch repair proteins was regarded as deficient mismatch repair. The deficient mismatch repair rate was 12.8%. Deficient mismatch repair appeared to be more frequent in the intestinal subtype of Lauren classification odds ratio (OR) = 4.767 (95% confidence interval [CI], 1.086-20.921; p = 0.039), tubular/papillary adenocarcinoma (OR = 5.25; 95% CI, 1.185-23.251; p = 0.029), mucinous adenocarcinoma (OR = 6.19; 95% CI, 1.113-34.445; p = 0.037), and differentiated type (OR = 3.24; 95% CI, 1.324-7.931; p = 0.01). No statistically significant association was detected with histopathological features according to the Tumor Location-Modified Lauren classification and mucinous secreting morphology. Deficient mismatch repair status was unusual in gastric cancer. The degree of cell differentiation and microscopic characteristics based on the World Health Organization and Lauren classification could all impact the predictive power for microsatellite-instable status.

Prognostic significance of microsatellite instability in patients with resectable gastric cancer

BACKGROUND

Microsatellite instability (MSI) gastric cancer (GC) generally has a better prognosis than microsatellite-stable (MSS) GC and has been associated with nonsurvival benefit with the addition of chemotherapy (CMT) compared with surgery alone. However, patients with MSI have distinct clinicopathological characteristics. This study aimed to compare the survival outcomes between patients with MSI GC and those with MSS GC. In addition, this study analyzed the survival outcomes of patients with MSI GC who received CMT.

METHODS

This study reviewed all patients with GC who underwent curative gastrectomy. Patients were divided into MSI group and the MSS group. Propensity score matching (PSM) was used to match clinicopathological factors.

RESULTS

Among the 378 patients enrolled, 78 (20.6%) had MSI. Older age (P < .001), subtotal gastrectomy (P = .008), pN0 (P = .020), and earlier pTNM stage (P = .012) were associated with MSI GC. Survival analysis showed better disease-free survival (DFS) and overall survival (OS) of patients in the MSI group (P = .012 and P = .019, respectively). After PSM, 78 patients were matched to each group. All variables assigned to the scores were well matched, and both groups became equivalent. After the matching, the differences in DFS and OS according to MSI/MSS status were estimated to be larger than before (DFS: 63.3% vs 41.4%; P = .002; OS: 65.8% vs 42.5%; P = .002). Regarding patients referred for CMT, there was no difference in DFS and OS between patients with MSI GC who underwent CMT and those who underwent surgery alone (P = .255 and P = .178, respectively).

CONCLUSION

Even after controlling for clinicopathological characteristics, MSI was identified as a prognostic factor for patient survival. MSI GC showed no significant survival benefit with the addition of CMT.

Microsatellite instability and mismatch repair protein deficiency: equal predictive markers?

Current clinical guidelines recommend mismatch repair (MMR) protein immunohistochemistry (IHC) or molecular microsatellite instability (MSI) tests as predictive markers of immunotherapies. Most of the pathological guidelines consider MMR protein IHC as the gold standard test to identify cancers with MMR deficiency and recommend molecular MSI tests only in special circumstances or to screen for Lynch syndrome. However, there are data in the literature which suggest that the two test types may not be equal. For example, molecular epidemiology studies reported different rates of deficient MMR (dMMR) and MSI in various cancer types. Additionally, direct comparisons of the two tests revealed relatively frequent discrepancies between MMR IHC and MSI tests, especially in non-colorectal and non-endometrial cancers and in cases with unusual dMMR phenotypes. There are also scattered clinical data showing that the efficacy of immune checkpoint inhibitors is different if the patient selection was based on dMMR versus MSI status of the cancers. All these observations question the current dogma that dMMR phenotype and genetic MSI status are equal predictive markers of the immunotherapies.