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

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<0.001). Neither TIL grade nor regression were protective of nodal metastasis or associated with improved survival. 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.