Tumor-infiltrating immune cell types predicting recurrence-free survival in melanoma patients receiving adjuvant PD-1 inhibitor therapy.

Background: Adjuvant treatment of melanoma patients with PD-1-based immunotherapy has improved recurrence rate, and became a standard treatment. However, a considerable proportion of patients recur within 1-2 years, necessitating the identification of predictive markers. Our study aimed to examine the association of intratumoral infiltration by specific immune cell subsets with the recurrence-free survival of melanoma patients receiving adjuvant PD-1 inhibitor therapy. Materials and methods: Archived paraffin blocks of pretreatment surgical samples from 48 melanoma patients receiving adjuvant PD-1 inhibitor therapy were selected. Intratumoral density of immune cells expressing the following markers: CD8, FOXP3, CD20, CD103, CD134, PD-1, and PD-L1 was determined by immunohistochemistry, and the associations with recurrence-free survival were analyzed. Results: Eighteen of the 48 patients developed recurrence during the follow-up period. In this group the ratio of patients showing strong immune cell infiltration (higher than the cutoff values defined by ROC curve analysis) was significantly lower compared to recurrence-free patients in the case of CD8 Conclusions: Our findings indicate the importance of immune cell infiltration in the efficacy of adjuvant PD-1 inhibitor treatment in a "real world" patient cohort.