POLE-mutant colon adenocarcinoma – case presentation and histopathological evaluation

Abstract

Abstract Introduction: POLE mutant phenotype in colon adenocarcinomas represents a rare molecular subtype. These tumours are generally responsive to immune-checkpoint inhibition therapy; therefore, are currently considered as a subtype with good prognosis. We hereby present the first detailed case presentation of a POLE mutant colon adenocarcinoma with useful microscopic features. Case report: A 53-year-old male patient’s colon adenocarcinoma showed wide variety of growth patterns and massive lymphocytic infiltrate. Immunohistochemistry revealed proficiency in mismatch repair proteins and SMARCB1 deficiency. Next-generation sequencing panel confirmed a pathogenetic mutation in POLE exon 9: p.Pro286Arg, c.857C>G. Conclusion: The diverse, high-grade morphology and increased intratumoral lymphoid infiltration should raise suspicion for POLE-mutated adenocarcinoma during everyday histopathological practice. Mismatch repair proficiency results on immunohistochemistry should not determine the final diagnosis, as only a minor percentage of these tumours are MSI. In every case suspicious for POLE-mutated adenocarcinoma, a 500-cancer gene panel should be carried out.