Occurrence, intratumoral heterogeneity, prognostic and predictive potential of microsatellite instability following surgical resection of primary colorectal carcinomas and corresponding liver metastases

Introduction: Besides clinicopathological parameters, molecular markers can be very important, and further characterize colorectal carcinomas into chromosomally unstable, microsatellite instable and "CqG-island methylator phenotype" groups. Aim: To study the frequency of microsatellite instability using immunohistochemical evaluation of MLH1, MSH2, MSH6 and PMS2 proteins in colorectal carcinoma. Method: 122 colorectal carcinomas as well as in 69 paired liver metastases were evaluated. Additionally, prognostic and predictive potential of mismatch repair status was tested. Results: Microsatellite instable phenotype was identified in 11.5% (14/122) of the tumours. There were no differences regarding staining intensity of tumour regions. Mismatch repair status was discordant in primaries vs. metastases in 20.2%. There was no difference in progression free- and overall survival according to mismatch repair status. The mismatch repair status was not predictive for survival within systemic therapy regimen groups. Conclusions: The subgroups of colorectal carcinomas could be evaluated in a larger and homogenised patient cohort to predict prognosis and response to therapy.