This is an open-label, non-randomized, Phase II study. Patients will be enrolled in 2 treatment arms (Arm A: IFX-1 monotherapy; Arm B: IFX-1 + pembrolizumab combination therapy), both consisting of 2 stages whereas Arm B starts with a safety run in portion. Enrollment follows an optimal Simon's 2-stage design with an interim analysis of treatment response after Stage 1 prior to patient enrollment into Stage 2.

Arm B will start after ≥3 patients have been treated in Arm A and no toxicity concerns have emerged. In a safety run-in part of Arm B, escalating doses of IFX-1 will be investigated in combination with pembrolizumab in order to identify the MTD or RP2D. Patients will be treated until progression, occurrence of unacceptable toxicity, or treatment discontinuation for any other reason.

Inclusion Criteria:

• At least 18 years of age on day of signing informed consent
• Patients with biopsy-proven, histologically or cytologically confirmed (a.) locally advanced cSCC not amenable for curative treatment or (b.) metastatic cSCC. Patients must have been treated with all approved therapies for (a.) inoperable locally advanced cSCC contraindicated for radiation therapy or (b.) metastatic cSCC
• Eastern Cooperative Oncology Group performance status (ECOG PS) status of ≤1
• Patients must have progressed on treatment with an anti-PD-1/L1 monoclonal antibody (mAb) administered either as monotherapy or in combination with other checkpoint inhibitors or other therapies.
• Patient provides written informed consent for the study.

Exclusion Criteria:

• Patients with limited cSCC, who do not require systemic therapy
• Has a diagnosis of immunodeficiency or autoimmune disease, or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 3 weeks prior the first dose of study treatment
• Has severe hypersensitivity (≥Grade 3) to pembrolizumab or IFX-1 and/or any of their excipients or had a severe (≥Grade 3) infusion-related reaction to treatments with other mAbs
• Patients who have undergone major surgery <4 weeks prior to starting study treatment
• Patients with known ≥Grade 3 (per National Cancer Institute common terminology criteria for adverse events [NCI CTCAE] v5.0 criteria) active systemic or cutaneous viral, bacterial, or fungal infection
• Has known active central nervous system metastases and/or carcinomatous meningitis.
• Patients with a history of other malignancies during the past 5 years
• Patients with congestive heart failure, Class III or IV, by New York Heart Association criteria
• Patients who are pregnant or breastfeeding or expecting to conceive or father children within the projected duration of the study,