• Signed written informed consent obtained prior to initiation of any study-specific procedures and treatment as confirmation of the patients awareness and willingness to comply with the study requirements.

• Female patients who are at least 18 years of age on the day signing informed consent

• Histologically confirmed locally advanced, recurrent, persistent and/or metastatic VSCC not amenable for salvage surgery or definitive (chemo)radiation (additive palliative radiotherapy for symptom control is allowed)

• ≤2 previous lines of chemotherapy for recurrent or metastatic disease

• Measurable disease (investigator assessed RECIST 1.1). Lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions.

• Have an eastern cooperative oncology group (ECOG) performance status of 0-1. Evaluation of ECOG is to be performed within 7 days prior to the first dose of study intervention.

• No pregnancy (as documented by a positive beta-human chorionic gonadotropin \[ß-hCG\] or human chorionic gonadotropin \[hCG\]) test with a minimum sensitivity of 25 IU/L or equivalent units of ß-hCG \[or hCG\]), no breastfeeding, and at least one of the following conditions applies:

‣ Not a woman of childbearing potential (WOCBP) as defined in Appendix 4 OR

⁃ A WOCBP who agrees to follow the contraception and pregnancy testing recommendations for investigational medicinal products (IMPs) with demonstrated or suspected human teratogenicity/ fetotoxicity in early pregnancy of the CTFG-guideline in Appendix 4 during the treatment period and for at least 4 months (corresponding to time needed to eliminate pembrolizumab) after the last dose of study treatment. In addition to the described highly effective oral/transdermal contraception methods a barrier method must be used.

• A WOCBP should not become pregnant during the treatment and for at least four months.

• Available archival tumor tissue sample and/or newly obtained core or excisional biopsy of a tumor lesion ideally not previously irradiated. Formalin-fixed, paraffin embedded (FFPE) tissue blocks are preferred to slides.

• Adequate organ function as defined in Table 3 of study protocol. Specimens must be collected within 10 days prior to the start of study treatment.