PD-L1 Expression in Mismatch Repair-deficient Endometrial Carcinomas, Including Lynch Syndrome-associated and MLH1 Promoter Hypermethylated Tumors

Am J Surg Pathol. 2017 Mar;41(3):326-333. doi: 10.1097/PAS.0000000000000783.


Mismatch repair (MMR)-deficient endometrial carcinomas (ECs) bearing Lynch syndrome (LS)-associated germline mutations or sporadic MLH1 promoter hypermethylation (MLH1hm) are highly immunogenic and may represent excellent candidates for therapies targeting the programmed cell death (PD)/programmed cell death ligand-1 (PD-L1) immune checkpoint pathway. This study evaluates PD-L1 expression in MMR-deficient ECs including LS-associated and MLH1hm cases, in comparison with MMR-intact tumors. Immunohistochemistry for PD-L1/CD274 was performed on 38 MMR-deficient and 29 MMR-intact ECs. Staining was scored in the tumor and the peritumoral immune compartment. The majority of MMR-deficient tumors were PD-L1 positive (53%) in at least a subset of tumor cells. LS-associated tumors were more likely to be PD-L1 positive relative to MLH1hm tumors (70% vs. 33%, P=0.05). Only 10% of MMR-intact ECs demonstrated any tumoral PD-L1 expression; this was significantly lower than was observed in MMR-deficient tumors (P=0.0005). When reviewed by histologic grade, PD-L1 expression remained highest in LS-associated ECs followed by MLH1hm and MMR-intact carcinomas, respectively. The MMR immunohistochemical pattern most uniformly associated with PD-L1 expression was MSH6 loss. Immune PD-L1 expression was seen in 100% of MMR-deficient and 66% of MMR-intact cases. This study represents the first to characterize differences in PD-L1 expression between LS-associated and MLH1hm endometrial cancers. It demonstrates that tumoral PD-L1 expression is more common in LS-associated endometrial cancers relative to MLH1hm and MMR-intact tumors, although sporadic cancers often show PD-L1 positive immune staining. These data suggest that MMR deficiency may be a better predictor of response to PD-1/PD-L1 inhibitor therapy than tumor grade in EC, and that potential benefit may vary based on the molecular mechanism of MMR defects.

MeSH terms

  • Aged
  • B7-H1 Antigen / metabolism*
  • Biomarkers, Tumor / genetics
  • Biomarkers, Tumor / metabolism*
  • Brain Neoplasms / genetics*
  • Brain Neoplasms / metabolism
  • Brain Neoplasms / mortality
  • Brain Neoplasms / pathology
  • Colorectal Neoplasms / genetics*
  • Colorectal Neoplasms / metabolism
  • Colorectal Neoplasms / mortality
  • Colorectal Neoplasms / pathology
  • Colorectal Neoplasms, Hereditary Nonpolyposis / genetics*
  • Colorectal Neoplasms, Hereditary Nonpolyposis / metabolism
  • Colorectal Neoplasms, Hereditary Nonpolyposis / mortality
  • Colorectal Neoplasms, Hereditary Nonpolyposis / pathology
  • DNA Methylation*
  • DNA Mismatch Repair
  • Endometrial Neoplasms / genetics*
  • Endometrial Neoplasms / metabolism
  • Endometrial Neoplasms / mortality
  • Endometrial Neoplasms / pathology
  • Female
  • Follow-Up Studies
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Immunohistochemistry
  • Middle Aged
  • MutL Protein Homolog 1 / genetics*
  • Neoplastic Syndromes, Hereditary / genetics*
  • Neoplastic Syndromes, Hereditary / metabolism
  • Neoplastic Syndromes, Hereditary / mortality
  • Neoplastic Syndromes, Hereditary / pathology
  • Prognosis
  • Promoter Regions, Genetic


  • B7-H1 Antigen
  • Biomarkers, Tumor
  • CD274 protein, human
  • MLH1 protein, human
  • MutL Protein Homolog 1

Supplementary concepts

  • Turcot syndrome