Patients with melanoma of unknown primary show better outcome under immune checkpoint inhibitor therapy than patients with known primary: preliminary results

Background: Melanoma of unknown primary (MUP) is an uncommon clinical subtype of melanoma of known primary (MKP). Objectives: We aimed to compare treatment outcomes of MUP and MKP patients who had undergone therapy with immune checkpoint inhibitors (ICPI). Methods: We studied 41 metastatic melanoma patients (32 with MKP and 9 with MUP) with an indication for ICPI. Results: Clinical characteristics such as age, gender, stage of disease, etc., did not significantly differ (P < .05) between MUP and MKP patients. 20/32 (62.5%) melanoma-specific deaths (MSD) were observed in the MKP group, whereas 2/9 (22.2%) were detected in the MUP group (P = .035). On logistic regression, the MUP status proved to be an independent predictor for a more favorable outcome under immunotherapy when compared to MKP (P = .030). Conclusion: Our preliminary results indicate that MUP patients show better clinical outcome under ICPI when compared to MKP.