A Retrospective, Observational Analysis of Tumor Infiltrating Lymphocytes and Tumor Regression in Melanoma.

ABSTRACT Background Tumor infiltrating lymphocytes (TILs) and regression are thought to be distinct markers of the immune response to melanoma. Objective This study sought to analyze the relationship of TIL grade and presence of regression to each other and to other prognostic histopathologic and clinical values in melanoma. Materials and Methods A retrospective analysis was conducted using patients diagnosed with melanoma between 2013 and 2019 whose complete histopathologic reports were available. Results Regression was seen in 48.9%, 30.1% and 37.9% of patients with brisk, non-brisk, and absent TILs respectively (P=0.019). Melanoma tumors with brisk TILs were found to have a lower Breslow thickness than those with non-brisk or absent (P= 0.001). Tumors with regression were also found to have lower Breslow thickness (P Conclusion Brisk TILs have a positive association with thinner tumors and the presence of tumor regression relative to non-brisk or absent TILs. This may suggest a more robust immune response in tumors with brisk TILs. Further exploration of the interplay between TIL grade, lymphocyte cell subtype and lymphocyte density may help explain this finding.