Immunohistochemical analysis of dna mismatch repair genes in colorectal carcinomas

Colorectal cancer/cancers (CRCa/CRCas) develop through three different major molecular pathways that we know today. One of these pathways, the microsatellite instability (MSI) pathway, is characterized by defects in DNA mismatch repair genes (MSH2, MSH6, MLH1, PMS2) and is responsible for approximately 15% of all CRCas. Clinicopathological features, prognosis and treatment of CRCas developing via by MSI are different from microsatellite stable tumors. MSI has also been described in serrated neoplasia pathway and colorectal precursor lesions in Lynch syndrome cases. The aim of our study was to analyze immunohistochemically DNA mismatch repair (MMR) gene expressions in our cases of CRCa and polpy and to reveal possible relationships between the gene expression statuses and clinicopathological parameters in CRCa cases. From the archive of Tokat Gaziosmanpaşa University Faculty of Medicine, Department of Pathology, 75 CRCas, 20 hyperplastic polyps (HP), 20 serrated polyps (SP), 20 low-grade dysplasia adenomatous polyps (LDAP), and 20 high-grade dysplasia adenomatous polyps (HDAP) cases were included in the study. Colonic mucosa samples within normal limits of 15 patients who underwent colonoscopy for non-tumor reasons was determined as the control group (CG). The CRCa group was divided into groups within itself. According to this; 15 cases of descending colon nonmucinous adenocarcinoma (DCNMCa), 14 cases of descending colon adenocarcinoma with mucin deposition (DCMCa), 15 cases of ascending colon nonmucinous adenocarcinoma (ACNMCa), 15 cases of ascending colon adenocarcinoma with mucin deposition (ACMCa), and 16 cases of neoadjuvant treated adenocarcinoma (ATCa) ) groups were created. The study was carried out on a total of 170 cases. Clinicopathological data of CRCa cases were obtained from our pathology report archive and hospital automation system. In addition to the clinicopathological data we reported as standard in CRCa cases, Crohn's-like reaction, mucinous component percentage and signet ring cell component were also evaluated and included in the analysis. Paraffin blocks and stained preparations obtained from the archive of all KRCa and polyp cases were reviewed. MSH2, MSH6, MLH1 and PMS2 immunohistochemical analyzes were performed on the sections prepared from the selected blocks in a fully automatic immunohistochemistry device. Significance test of the difference between two means, one-way analysis of variance and chi-square tests were used in statistical analysis. Statistically significant correlation was accepted at p<0.05. A ready-made statistical software program was used for the calculations (SPSS 22.0 Chicago, IL, USA). In the general CRCa group, the male/female ratio was 1.5, the mean age was 65.1 years, and the mean tumor diameter was 49.1 mm. In our CRCa group, MSH2, MSH6, MLH1 and PMS2 expression losses were observed at the rates of 11.8%, 9.6%, 40.9% and 33.9%, respectively. Co-expression losses of MSH2/MSH6 and MLH1/PMS2 were seen at rates of 8.8% and 31%, respectively. For the majority of MMR proteins (MSH2, MSH6, PMS2 and MSH2/MSH6), the highest rates of expression losses in tumors with a right colon mucinous component (ACMCa) (35.7%, 35.7%, 66.7% and 35.7%, respectively) were observed (p<0.05). Losses of PMS2, MSH2/MSH6 and MLH1/PMS2 expressions were seen significantly more frequently in right colon tumors (p<0.05). Tumors with loss of MSH6 expression had a larger mean diameter (64.4 mm vs. 47 mm) (p<0.05). Tumors showing loss of PMS2 and MLH1/PMS2 expression were more prone to low-grade differentiation (p<0.05). The rates of cases with extracellular mucin, Crohn's-like reaction and signet ring cell component were higher in tumors with loss of MMR expression. The losses rates of all MMR expressions were significantly different between groups (for all; p<0.05). The highest MSH2, MSH6, PMS2, MSH2/MSH6 and MLH1/PMS2 expression losses were in the ACMCa group (35.7%, 35.7%, 66.7%, 35.7% and 66.7%, respectively) while the highest MLH1 expression loss was seen in the ATCa group (60%). Among polyps, the highest losses of MSH2 and MSH6 expression were observed in the SP group (10% for both), while the highest expression losses of MLH1, PMS2 and MLH1/PMS2 were found in the HDAP group (15.8%, 10% and 5.9%, respectively). The highest loss of MSH2/MSH6 expression was found in the SP and HDAP groups with 5.6%. The expression losses were also remarkable in our control group (6.7%, 7.1%, 9.1% for MSH6, MLH1 and PMS2, respectively). The results of our study were generally compatible with the literature in terms of loss of MMR protein expression in colorectal neoplasms, but also showed some differences. First of all, our rates of MLH1 and PMS2 expression losses were very high compared to the literature. The highest rate of loss of MMR protein expression was observed in right colon tumors with mucinous component, while increased tumor diameter, mucin content, signet ring cell component, and Crohn's-like reaction were observed in higher rates in tumors with MMR expression loss. On the other hand, the degree of histological differentiation was found to be lower in our tumors with MMR loss, contrary to the literature. In our series, MMR expression losses in polyp groups were generally lower than carcinomas (especially in the right colon tumors with mucinous component) consistent with the literature. We can say that the histopathological features associated with MSI-H tumors in the literature are generally valid for our cases as well. In addition, the higher rates of MMR expression losses in our series (including the control group) seem to be due to technical reasons. In particular, it is understood that better standardization of tissue fixation can yield more consistent results with the literature. Key words: colorectal carcinoma, polyp, MSI, MMR protein expression, immunohistochemistry.