Abstract

Colorectal carcinomas (CRC) with mismatch repair (MMR) deficiency have increased tumor mutation burden and respond to immune checkpoint inhibitor therapy. The Cancer Genome Atlas identified hypermutated CRCs with somatic mutations in DNA polymerase e (POLE) with mutation burdens exceeding that of MMR-deficient CRCs.To identify the morphologic, immunophenotypic and molecular features of POLE mutated CRCs, 63 consecutive MMR-intact CRCs were evaluated by Sanger sequencing for POLE exonuclease domain mutations in exons 9, 11, 13 and 14 and confirmed by next generation sequencing. Tumor immune microenvironment and immunoscores were assessed in POLE-mutated CRCs using immunohistochemistry to detect CD3+/CD8+ tumor-infiltrating lymphocytes and compared to 59 non-POLE mutated MMR-intact CRC, 10 non-POLE mutated MMR-deficient CRCs, and 223 normal colonic mucosa.4.8% CRC (4 MMR-intact primary and 1 MMR-intact metastasis) harbored POLE mutations in amino acid 286 in exon 9 (p.P286R) or exon 13 (p.V411L). POLE mutated CRCs arose in the transverse colon and rectum, were male-predominant, younger, and showed increased tumor-infiltrating lymphocytes and immune cells at the tumor-stromal interface. The patient with metastatic POLE mutated CRC was placed on PD-1 inhibitor treatment with marked and sustained response. These data indicate that POLE mutated CRCs have hypermutated phenotypes despite MMR-intact status, with mutation burdens higher than that in microsatellite unstable CRCs. Given the recent approval for treatment of microsatellite unstable cancer with immune checkpoint inhibitors, assessment of POLE status may help guide therapeutic decisions for hypermutated tumors with intact MMR that would otherwise be missed by routine testing.

View details for DOI 10.1111/his.13984

View details for PubMedID 31479159