RM-1995 Photoimmunotherapy, as Monotherapy or Combined With Pembrolizumab, in Patients With Advanced CuSCC and HNSCC

* Inclusion Criteria. Patients must meet all the following criteria to be eligible to participate in the study: * Patient must be at least 18 years old. * Patient must have tumor types of head and neck squamous cell carcinoma (HNSCC), cutaneous squamous cell carcinoma (cuSCC) * Locally advanced or locoregional disease that has recurred or progressed on or after at least one prior line of therapy, which must include prior platinum-based chemotherapy, and is not eligible for further locoregional treatment (ie, standard surgery or radiation), or for which locoregional treatment has proved to be intolerable or is medically contraindicated. * Metastatic disease that has recurred or progressed following prior platinum-based chemotherapy, prior immunotherapy with PD-(L)1 inhibitors, or other standard of care systemic treatment, has proven to be ineffective, intolerable, or is considered medically contraindicated in the opinion of the Investigator * Patient must have tumors with at least one superficial lesion of the skin or oral cavity, not deeper than 1 cm and that is accessible for photoimmunotherapy treatment. Note: Lesions that are in the pharynx and larynx will not be included in the treatment. * Patient must have the ability to provide representative tumor specimens with an associated pathology report. * Patient must have measurable disease by RECIST 1.1 as assessed by Investigator. * Patient must have ECOG performance status of 0 to 2 at the time of screening * Patient has life expectancy ≥ 3 months based on Investigator's judgement. * Adequate organ function laboratory values (Hematology, Hepatic, Renal and Coagulation). * Female patients of childbearing potential must not be pregnant or breastfeeding and must be willing to use 2 methods of highly effective birth control, or practice abstinence throughout the study and for at least 120 days after the last dose of study medication. * Male patients must be sterile or agree to use an adequate method of contraception or practice abstinence starting with the first dose of study medication and for at least 120 days after the last dose of study medication. Exclusion Criteria. Patients who meet any of the criteria below will be ineligible to participate in the study: * Receiving any other investigational agents, approved anticancer therapies, including chemotherapy, hormonal therapy, ultraviolet-light therapy, or other topical therapy within 2 weeks or 5 half-lives, whichever is longer, before initiation of study treatment, with the following exceptions: * Hormone-replacement therapy or oral contraceptives * Herbal therapy, including herbal therapy intended as anticancer therapy and medicinal cannabinoids taken to reduce symptom burden, must be discontinued at least 1 week before the first dose of pembrolizumab (combination therapy) or the first dose of RM-1995 (monotherapy) * Palliative radiotherapy for painful boney metastases or metastases in potentially sensitive locations (eg, epidural space) must be completed \> 2 weeks before the first dose of pembrolizumab (combination therapy) or the first dose of RM 1995 (monotherapy) * Previously initiated bisphosphonate or denosumab therapy for bone metastases may be continued during study participation. * Treated with local radiation therapy within 12 weeks before the first dose of study treatment. Patients must have recovered from all radiation-related toxicities to Grade \< 1 or baseline and must not require steroids. * Treatment with systemic immunostimulatory agents not described above (including but not limited to IFN-α, IL-2) within 6 weeks or 5 half-lives of the drug, whichever is shorter, before the first dose of study treatment. * Adverse events from prior anticancer therapy that have not resolved to Grade ≤ 1, except for alopecia or endocrinopathy managed with replacement therapy. * Patients who have tumors at sites that may compromise sensitive and vital anatomic structures. * Malignancies other than disease under study within 3 years prior to treatment start, except for those with a negligible risk of metastasis or death. * Significant cardiovascular disease, such as New York Heart Association cardiac disease (Class II or greater), myocardial infarction within the previous 3 months, unstable arrhythmias, or unstable angina. * Known clinically significant liver disease, including active viral, alcoholic, or other hepatitis, cirrhosis, or inherited liver disease. * Prior allogeneic bone marrow transplantation or prior solid organ transplantation. * Known history of testing positive for human immunodeficiency virus or acquired immunodeficiency syndrome -related illness. * Known infection or detection of active Hepatitis B (e.g., HBsAg positive), Hepatitis C (eg, RNA \[qualitative\]), or SARS-CoV-2 (qualitative). * Received a live, attenuated vaccine within 4 weeks before the first dose of study treatment or anticipating the receipt of a required live, attenuated vaccine during the study (based on known medical history). * Receiving drugs known to prolong the QTc interval while on study treatment or within 14 days before the first dose of study treatment. * Receiving cytochrome P450 (CYP) substrates, inhibitors, inducers while on study treatment or within 14 days before the first dose of study treatment. * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or poorly controlled psychiatric illness. * Received oral or IV antibiotics within 2 weeks before the first dose of study treatment * Major surgery or significant traumatic injury within 28 days before the first dose of study treatment or anticipation of the need for major surgery that is unrelated to study intervention during the study. * History of severe allergic, anaphylactic, or other hypersensitivity reactions to any of the components of RM-1995 or to other recombinant chimeric, human, or humanized antibodies.