Pembrolizumab for Advanced Cutaneous Sarcomas Not Including Angiosarcoma

Inclusion Criteria: * Male/female participants who are at least 18 years of age on the day of signing informed consent with histologically confirmed diagnosis of soft tissue sarcoma, not including angiosarcoma, will be enrolled on study. The primary tumor site must be deemed to be cutaneous or dermal in the opinion of the treating investigator (note the primary tumor site does NOT need to be present at the time of screening, i.e., may have been previously resected but recurred and/or metastasized). * Participants must have metastatic or advanced disease which could include recurrent, unresectable or multifocal lesions or in which resection would result in unacceptable morbidity per the treating investigator. * Have measurable disease based on RECIST 1.1. Lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions. * Archival tumor tissue sample or newly obtained \[core, punch, incisional, or excisional\] biopsy of a tumor lesion not previously irradiated is available. Formalin-fixed, paraffin embedded (FFPE) tissue blocks are preferred to slides. Newly obtained biopsies are preferred to archived tissue. * Prior oncologic therapy is allowable but not required. Must be at least 4 weeks since prior systemic anti-cancer therapy including investigational agents prior to start of study treatment. For prior tyrosine kinase inhibitor therapy, 3 drug half-lives may instead be used for this criterion (if shorter). Mus…