Intertumoral Heterogeneity of CD3 and CD8 T-Cell Densities in the Microenvironment of DNA Mismatch-Repair-Deficient Colon Cancers: Implications for Prognosis.

PURPOSE

Colorectal cancers with deficient DNA mismatch repair (dMMR) are presumed to uniformly have dense lymphocytic infiltration that underlies their favorable prognosis and is critical to their responsiveness to immunotherapy, as compared with MMR-proficient (pMMR) tumors. We examined T-cell densities and their potential heterogeneity in a large cohort of dMMR tumors.

EXPERIMENTAL DESIGN

CD3 and CD8 T-cell densities were quantified at the invasive margin (IM) and tumor core (CT) in 561 stage III colon cancers (dMMR, = 278; pMMR, = 283) from a phase III adjuvant trial (N0147). Their association with overall survival (OS) was determined using multivariable Cox analysis.

RESULTS

Although CD3 and CD8 T-cell densities in the tumor microenvironment were higher in dMMR versus pMMR tumors overall, intertumoral heterogeneity in densities between tumors was significantly higher by 30% to 88% among dMMR versus pMMR cancers ( < 0.0001 for all four T-cell subtypes [CD3IM, CD3CT, CD8IM, CD8CT]). A substantial proportion of dMMR tumors (26% to 35% depending on the T-cell subtype) exhibited T-cell densities as low as that in the bottom half of pMMR tumors. All four T-cell subtypes were prognostic in dMMR with CD3IM being the most strongly prognostic. Low (vs. high) CD3IM was independently associated with poorer OS among dMMR (HR, 4.76; 95% confidence interval, 1.43-15.87; = 0.0019) and pMMR tumors ( = 0.0103).

CONCLUSIONS

Tumor-infiltrating T-cell densities exhibited greater intertumoral heterogeneity among dMMR than pMMR colon cancers, with CD3IM providing robust stratification of both dMMR and pMMR tumors for prognosis. Potentially, lower T-cell densities among dMMR tumors may contribute to immunotherapy resistance.