Study сomparing the Efficacy and Safety of RPH-075 and Keytruda® in Patients With Unresectable or Metastatic Skin Melanoma

This study will include the following periods: 1. Screening period (before the first administration of the test drug). Before being included in the study, patients will be provided with complete information about this clinical trial, its objectives, as well as the risks associated with participating in it, as set out in the patient information sheet. After the patient signs the Informed consent Form (IF), he will be examined as part of the screening period, at the end of which the researcher will decide whether or not the patient can be randomized into the study. 2. Main period (days: 1 - 168) Patients who meet the selection criteria will be randomized in a 1:1 ratio to one of the two study groups: RPH-075 and Keytruda®. Patients will receive pembrolizumab (RPH-075 or Keytruda®) in a monotherapy regimen, at a dose of 200 mg, intravenously, with a frequency of once every 3 weeks (3 weeks - 1 cycle). Therapy within the Main Study period will continue until (whichever comes first): * 24 weeks (8 cycles, 168 days); * disease progression (according to the Immune-Related Response Evaluation Criteria In Solid Tumors (iRECIST)/clinical progression); * the development of phenomena of intolerable toxicity. The assessment of tumor response to the therapy at this step will be carried out every 12 weeks. 3. Continued therapy period (days: 169 - 365) During the period of continued therapy, all patients will receive therapy with RPH-075, including those patients who received therapy with Keytruda® during the Main Study Period. Pembrolizumab will be administered intravenously, at a dose of 200 mg, with a frequency of once every 3 weeks. In case of significant AEs, pembrolizumab therapy may be postponed for up to 12 weeks. Therapy within the period of continued therapy will be carried out until (whichever comes first): * a period of up to 1 year; * before the disease progression (according to the criteria of iRECIST /clinical progression); * the development of phenomena of intolerable toxicity. The assessment of tumor response to the therapy at this step will be carried out every 12 weeks. 4. The period of further treatment (days: 366-730\]) Participants in this period will be patients who, after 1 year of therapy, will have a stabilization of the disease or a tumor response to therapy. The decision to switch to this period wil be made by the researcher. If, according to the decision of the researcher, the patient will not be recommended to switch to this period, then the patient goes into the Follow-up Period. During the the period of further treatment patients will receive therapy with RPH-075 according to the same scheme as in the period of Continued therapy. Therapy within the Period will be carried out until (whichever comes first): * a total period of up to 2 years; all examinations will be carried out within the framework of routine clinical practice; * before the disease progression; * the development of phenomena of intolerable toxicity. All examinations necessary for the patient, including radiation diagnostics, and concomitant therapy during the Period will be carried out within the framework of routine clinical practice and through the healthcare system, with the exception of visits where therapy will be administered (every 3 weeks). Also, during these visits, data on the AEs and occurrence of events (progression) will be collected. 5. Follow-up period (FU) For patients who will have completed their planned participation, namely: * The period of further treatment, * The period of continued therapy (those patients who will not be transferred during the pre-treatment Period), one follow-up visit (FU-visit) will be scheduled 28 ± 3 days after the last administration. For patients who will complete therapy ahead of schedule (within the Main period or the Period of continued therapy), due to the progression of the disease or the development of intolerant toxicity phenomena, FU visits will be conducted with a multiplicity of 1 every 12 weeks until the Day 365 of the study. All examinations and concomitant therapy during the Follow-up Period will be provided through the health care system (as a part of routine clinical practice), with the exception of a radiation diagnostic visit conducting to assess the response (every 12 weeks). The total expected duration of the study is approximately 3 years. The expected duration of participation of each subject is approximately 26 months (about 2 years).