Phase Ib/II open-label, multi-center study with a priming cycle of 4SC-202 to evaluate the safety, tolerability and preliminary efficacy of combination treatment with 4SC-202 and Pembrolizumab. A dose expansion cohort at the Recommended Phase Two Dose (RPTD) will be added.

Adult patients with advanced (unresectable or metastatic) cutaneous melanoma primary refractory or non-responding to anti-PD-1 therapy as most current systemic anti-cancer therapy and for whom no standard therapy is available, will be enrolled. The last administration of anti-PD-1 therapy must have been performed within 6 months prior to screening.

Main Inclusion Criteria:

• Patients with unresectable stage III or stage IV cutaneous melanoma, as per American Joint Committee on Cancer (AJCC) (Version 8) staging system (must have been histologically confirmed at least once during course of disease). Patients with metastatic tumor of unknown primary site and histology of melanoma are eligible.
• Patients must be primary refractory or non-responding to anti-PD-1 therapy (either as monotherapy or in combination with Ipilimumab)
• Measurable disease by computer tomography (CT) or Magnetic resonance imaging (MRI) per immune-related response evaluation criteria in solid tumors (irRECIST) 1.1 criteria, with longest diameter for non-nodal lesions ≥ 10 mm and ≥ 15 mm in short axis for nodal lesions
• At least one tumor site (either primary site or metastasis) must be accessible for sequential biopsies and patient must consent to the 2 mandatory biopsies. This requirement is not applicable for continuous dosing schedules and may be waived by the sponsor in other individual cases.

Main Exclusion Criteria:

• Patients who achieved a CR or PR, during or after prior anti-PD-1 mono- or anti-CTLA-4/anti-PD-1 combination therapy
• Patients with symptomatic brain metastases/central nervous system (CNS) involvement
• Patients with inadequate organ function
• Therapy with agents known to prolong the QT interval and increase the risk for Torsades de Pointes