[Association of status of mismatch repair protein expression and EB virus infection with clinicopathological parameters in 886 gastric adenocarcinoma patients].

Objective: To analyze the expression of mismatch repair (MMR) protein and the EB virus infection in gastric adenocarcinoma, and to examine the association of MMR expression and EB virus infection with clinicopathological parameters. Methods: A case-control study was performed. Clinicopathological data of patients who was pathologically diagnosed as gastric adenocarcinoma, received radical gastrectomy and had complete clinicopathological data from August 2017 to April 2020 in Tianjin Medical University Cancer Institute and Hospital were retrospectively collected and analyzed. The immunohistochemistry (IHC) of MMR proteins and in situ hybridization (ISH) of Epstein-Barr virus encoded RNA (EBER) were reviewed. The associations of MMR and EBER results with clinicopathological parameters were analyzed. The main observations of the study were MMR and EBER expression, and association of MMR and EBER results with clinicopathological parameters. Results: Eight hundred and eighty-six patients were enrolled, including 98 patients who received preoperative neoadjuvant chemoradiotherapy. Of 886 patients, 613 (69.2%) were males and the median age was 60 (22-83) years; 831 (93.8%) were mismatch repair proficiency (pMMR), and 55 (6.2%) were mismatch repair deficiency (dMMR). In dMMR group, 47 cases (85.5%) had the deficiency of both MLH1 and PMS2, 1 case (1.8%) had the deficiency of both MSH2 and MSH6, 4 cases (7.3%) had the deficiency only in PMS2, 2 cases (3.6%) had the deficiency only in MSH6, and 1 case (1.8%) had the deficiency only in MSH2. The deficiency rates of PMS2, MLH1, MSH6 and MSH2 were 5.8% (51/886), 5.3% (47/886), 0.3% (3/886) and 0.2% (2/886), respectively. Among the 871 cases with EBER results, 4.9% (43/871) were positive EBER. Univariate analysis showed that dMMR was more frequently detected in female patients (χ(2)=10.962, P=0.001), cancer locating in the antrum (χ(2)=9.336,P=0.020), Lauren intestinal type (χ(2)=9.718, P=0.018), stage T3 (χ(2)=25.866, P<0.001) and TNM stage II (χ(2)=15.470, P=0.002). The ratio of dMMR was not significantly associated with age, tumor differentiation, histological type, lymph node metastasis, distant metastasis or Her-2 immunohistochemical score (all P>0.05). Compared with negative EBER, positive EBER was more frequent in male patients (χ(2)=9.701, P=0.002), cancer locating in gastric fundus and corpus (χ(2)=17.964, P<0.001), gastric cancer with lymphoid stroma (χ(2)=744.073, P<0.001) and poorly differentiated cancer (χ(2)=13.739, P=0.010). Positive EBER was not significantly associated with age, depth of invasion, lymph node metastasis, distant metastasis, TNM stage or Her-2 immunohistochemical score (all P>0.05). In addition, all dMMR cases were EBER negative, and all cases of positive EBER were pMMR. Conclusions: The positive EB virus status is mutually exclusive with dMMR, indicating that different molecular subtypes of gastric adenocarcinoma are involved in different molecular pathways in tumorigenesis and progression. The overlapping of dMMR or positive EBER status and positive Her-2 expression is found in some cases of gastric adenocarcinoma. Patients with gastric adenocarcinoma after radical surgery should be tested for MMR status if they are female, the tumor locates in gastric antrum, the TNM staging is stage II or T3, or if the Lauren classification is intestinal type. And if patients are male, the tumor locates in the gastric fundus and corpus, the cancer is lymphoid stroma, or poor differentiated, the expression of EBER should be detected. Results of our study may provide evidence for further decision-making of clinical treatment.

[Mismatch repair protein expression of colorectal cancer: a retrospective analysis of 3 428 cases].

Objective: To analyze the expression of mismatch repair (MMR) proteins in colorectal cancers (CRC) and to evaluate the feasibility and potential pitfalls of immunohistochemistry (IHC) analysis for MMR. Methods: The IHC sections for MMR proteins were reviewed in 3 428 cases of resected CRC without neoadjuvant therapy at Tianjin Medical University Cancer Institute and Hospital from July 2014 to October 2018. For the cases with unclear MMR IHC results during the initial review, IHC staining was repeated and microsatellite instability (MSI) analysis was performed. Relationships between the expression of MMR proteins and MSI status as well as the clinicopathological parameters were analyzed. Results: IHC staining for MMR was repeated in 28 (0.8%) cases due to poor quality of original IHC sections. Inconsistent results between the original diagnosis and re-diagnosis were found in 119 (3.5%) cases, mainly resulting from PMS2 and MLH1. Finally, 261 (7.6%) cases of CRC showed mismatch repair deficiency (dMMR), mainly from the deficiency of both MLH1 and PMS2 (43.3%,113/261). In the 14 cases with MSI results, the concordant of MSI and MMR was 13 cases. In the 29 dMMR cases with next generation sequencing (NGS) results, the concordant of MSI-high and dMMR was 93.1%(27/29). The cases with inconsistent results between MSI and MMR showed negative expression of MSH6 or PMS2. Twenty-one CRC showed negative expression of MLH1 and partially positive (or weak positive) expression of PMS2, or negative expression of MSH2 and partially positive (or weak positive) expression of MSH6. Among the 19 cases with MSI results, 16 cases were MSI-high, two cases were MSI-low, and one case was microsatellite stable. Compared with mismatch repair proficiency (pMMR), dMMR was more frequently detected in female patients younger than 50 years old, with family history, at early stage (Ⅰ-Ⅱ) CRC, and in the tumors from right colon,with poor differentiation, or mucinous adenocarcinoma/signet ring cell carcinoma (all P<0.05). Conclusions: At present, IHC staining is a clinically effective and convenient method to detect MMR expression, but the operating process and result assessment remain variable and need to be standardized. MSI analysis can be performed in the difficult-to-evaluate cases for MMR to enhance prognostic evaluation and treatment option.