PD-L1 expression, immune cell correlates, and PD-1+ lymphocytes in sentinel lymph node positive melanoma patients: Implications for adjuvant PD-1 clinical trials.

e20011 Background: Patients with positive sentinel lymph node biopsies (SLNB) that undergo a completion lymphadenectomy have variable five-year survival rates ranging from 39-70%. PD-1 and PD-L1 inhibitors have significantly improved recurrence free (RFS) and overall survival (OS) in AJCC stage IIIC/IV metastatic melanoma patients. The aims of this study were to characterise subpopulations of lymphocytes that interact with metastatic melanoma cells in SLNB, to determine tumoral PD-L1 expression and to identify whether the PD-1/PD-L1 pathway contributes to immune escape in these patients to provide a rationale for the use of anti-PD-1 inhibitors in the adjuvant setting and aid in the selection of patients for this treatment modality. Methods: The metastatic melanoma containing SLNB’s from sixty treatment-naive patients were analysed for CD3, CD4, CD8, FOXP3, PD-1, and PD-L1 and correlated clinico-pathologic features and outcome. Results: Tumoral PD-L1 expression ( ≥ 1%-cutoff) was present in 43.3% (n = 26)...