title: PD-L1 expression in colorectal cancer is associated with microsatellite instability, BRAF mutation, medullary morphology and cytotoxic tumor-infiltrating lymphocytes.
abstract: Programmed cell death 1 (PD-1) and its ligand (PD-L1) are key suppressors of the cytotoxic immune response. PD-L1 expression on tumor cells may be induced by the immune microenvironment, resulting in immune escape (adaptive immune resistance), and an adverse prognosis in many malignancies. In colorectal carcinoma the response to PD-1/PD-L1 inhibition is correlated with microsatellite instability. However, little is known about the clinicopathologic, molecular, and prognostic characteristics of colorectal carcinoma with PD-L1 expression. We performed immunohistochemistry for PD-L1 on 181 cases of colorectal carcinoma with known microsatellite instability and mutational status, and correlated PD-L1 expression with clinicopathologic features including tumor-infiltrating lymphocyte burden/immunophenotype, tumor mutational profile, and disease-specific survival. PD-L1 was expressed in tumors from 16 patients (9%) who were more often older (P=0.006) and female (P=0.035), with tumors exhibiting a larger size (P=0.013), but lower stage (P<0.001). PD-L1 expression was associated with increased CD8 and TBET-positive tumor-infiltrating lymphocytes, medullary phenotype, poor differentiation, microsatellite instability, BRAF mutation (P<0.001 for each), and a lower frequency of KRAS mutation (P=0.012). On multivariate analysis, PD-L1 expression was associated with medullary morphology and frequent CD8-positive tumor-infiltrating lymphocytes, suggesting adaptive immune resistance. PD-L1 positivity was not predictive of survival in the entire cohort, but it was associated with a lower disease-specific survival within the microsatellite-instability high cohort. PD-L1 expression in colorectal carcinoma is associated with clinicopathologic and molecular features of the serrated pathway of colorectal carcinogenesis, and is associated with a worse outcome within microsatellite-unstable tumors. These findings support the role of PD-L1 expression in providing normally immunogenic colorectal carcinoma a means of immune evasion and a more aggressive biology, provide a potential mechanistic explanation for the favorable response of microsatellite-unstable colorectal carcinoma to PD-1/PD-L1 pathway blockade, and suggest potential predictive and prognostic roles of PD-L1 immunohistochemistry in colorectal carcinoma.
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Rosenbaum
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Jacob R
authors.initials: JR
authors.lastname: Bledsoe
authors.affiliation: Department of Epidemiology and Biostatistics, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
authors.forename: Vicente
authors.initials: V
authors.lastname: Morales-Oyarvide
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Tiffany G
authors.initials: TG
authors.lastname: Huynh
authors.affiliation: Department of Pathology, Massachusetts General Hospital, Boston, MA, USA.|Department of Pathology, Harvard Medical School, Boston, MA, USA.
authors.forename: Mari
authors.initials: M
authors.lastname: Mino-Kenudson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D060890:B7-H1 Antigen / Q000032:analysis*; D014408:Biomarkers, Tumor / Q000032:analysis* / Q000235:genetics*; D016009:Chi-Square Distribution; D015179:Colorectal Neoplasms / Q000235:genetics / Q000276:immunology* / Q000401:mortality / Q000473:pathology; D004252:DNA Mutational Analysis; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D053208:Kaplan-Meier Estimate; D016015:Logistic Models; D016246:Lymphocytes, Tumor-Infiltrating / Q000276:immunology* / Q000473:pathology; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D015999:Multivariate Analysis; D009154:Mutation; D009367:Neoplasm Staging; D016017:Odds Ratio; D016016:Proportional Hazards Models; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D012307:Risk Factors; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000473:pathology; D047368:Tumor Burden; D019139:Tumor Escape; D059016:Tumor Microenvironment; D055815:Young Adult
chemical_list: D060890:B7-H1 Antigen; D014408:Biomarkers, Tumor; C423236:CD274 protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf