A Phase II Clinical Trial on Neo-adjuvant Pembrolizumab in Patients With pT3b-T4a/b cN0M0 Melanoma.

Inclusion Criteria: ≥ 18 years of age on the day of signing the informed consent. Histologically confirmed high risk primary cutaneous pT1b-4b melanoma High risk primary melanoma is defined in this study as the following AJCC8 T-stages: * pT1b-3a, with a poor prognostic score on the Merlin™ test ("Merlin™ high risk"); * pT3b-4b, irrespective of their Merlin™ test result Amendable to sentinel lymph node biopsy. No evidence of metastatic dissemination as demonstrated by PET/CT, ultrasound of the draining lymph node basin, and clinical examination. No prior exposure to systemic treatment for melanoma (adjuvant or curative). Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) of 0, 1 or 2 assessed within 7 days prior to the first dose of study treatment. Adequate baseline organ function as defined by local institutional standards. Women: * Female patients must be surgically sterile or be postmenopausal (A postmenopausal state is defined as no menses for 12 months without an alternative medical cause). * If a female patient is a woman of childbearing potential (WOCBP) they must agree to use highly effective contraception measures during the period of therapy, which should be continued for at least 4 months following the last dose of pembrolizumab as indicated in the SmPC. A list of highly effective contraceptive measures is included in appendix 1 All female patients with reproductive potential must have a negative pregnancy test (serum or urine) prior to enrollment and pregnancy testing should be conducted within 24h prior to the first dose of immune checkpoint inhibitors and thereafter monthly until 4 months following the last dose study treatment. * Should not be breastfeeding at screening or during study treatment. Men with a female partner of childbearing potential must agree to use highly effective contraception from 14 days prior to administration of the first dose of study treatment or have either had a prior vasectomy, throughout the treatment period, and for 16 weeks after the last dose of study treatment. Capable of providing documented informed consent, which includes compliance with the requirements and restrictions listed in the ICF and in this protocol. Exclusion Criteria: Patients with uveal melanoma, mucosal melanoma and melanoma of unknown primary origin. Active autoimmune disease requiring systemic treatment. Patients with a history of previous malignancies (except non-melanoma skin cancers, and the following in situ cancers: gastric, colon, cervical/dysplasia, melanoma, or breast) are excluded unless a complete remission was achieved at least 3 years prior to screening and no additional therapy is required or anticipated to be required during the study period. Known Human Immunodeficiency Virus (HIV), hepatitis B virus (HBV), or hepatitis C virus (HCV) infection. Exception: subjects with laboratory evidence of cleared HBV and HCV infection will be permitted. Any serious or unstable pre-existing medical conditions (aside from malignancy exceptions specified above), psychiatric disorders, or other conditions that could interfere with the subject's safety, obtaining informed consent, or compliance with study procedures. Active infection at the time of screening (e.g. wound infection). Known immediate or delayed hypersensitivity reaction or idiosyncrasy to drugs chemically related to the study treatment, or excipients. History of organ allograft. Patients who have previously been exposed to checkpoint inhibitors. Prior transplantation of human cells, tissues and organs (e.g. liver transplant) or candidates for any type of transplantation. History or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the trial, interfere with the patient's participation for the full duration of the trial, or is not in the best interest of the patient to participate, in the opinion of the treating investigator. Known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial. Any contra-indication for evaluation by whole body 18F-FDG-PET/CT or MRI.