Purpose Biomarkers for outcome after immune-checkpoint blockade are strongly needed as these may influence individual treatment selection or sequence. We aimed to identify baseline factors associated with overall survival (OS) following pembrolizumab treatment in melanoma patients. Experimental design Serum lactate dehydrogenase (LDH), routine blood count parameters, and clinical characteristics were investigated in 616 patients. Endpoints were OS and best overall response following pembrolizumab. Kaplan-Meier analysis and Cox regression were applied for survival analysis. Results Relative eosinophil count (REC) ≥1.5%, relative lymphocyte count (RLC) ≥17.5%, ≤2.5-fold elevation of LDH, and the absence of metastasis other than soft-tissue/lung were associated with favorable OS in the discovery (n=177) and the confirmation (n=182) cohort and had independent positive impact (all P<0.001). Their independent role was subsequently confirmed in the validation cohort (n=257; all P<0.01). The number of favorable factors was strongly associated with prognosis. One-year-OS probabilities of 83.9% vs 14.7% and response rates of 58.3% vs 3.3% were observed in patients with four out of four compared to those with none out of four favorable baseline factors present, respectively. Conclusions High REC and RLC, low LDH, and absence of metastasis other than soft-tissue/lung are independent baseline characteristics associated with favorable OS of patients with melanoma treated with pembrolizumab. Presence of four favorable factors in combination identifies a subgroup with excellent prognosis. In contrast, patients with no favorable factors present have a poor prognosis, despite pembrolizumab, and additional treatment advances are still needed. A potential predictive impact needs to be further investigated.

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