Background: Treatment options for recurrent and/or metastatic (R/M) salivary gland cancer (SGC) are limited with response rates to standard cytotoxic chemotherapy (CT) low at 10-30%, and responses to single-agent immune checkpoint inhibition (ICI) <10%. Current therapeutic agents used to treat R/M SGC have an unfavorable toxicity profile including cytotoxic CTs such as cisplatin and doxorubicin and the targeted therapy lenvatinib. Treatments with general applicability and acceptable side effect profile are urgently needed. Pemetrexed (PTX) is a multi-targeted anti-folate CT with an excellent safety and toxicity profile with promising responses reported in a case series of patients (pts) with R/M SGC (Viscuse P and Price K. Marked responses to pemetrexed chemotherapy for metastatic adenocarcinoma of the parotid gland: case series. Head Neck 2019;41(6):E99-103.). As the combination of PTX and pembrolizumab (PMB) showed enhanced responses and survival in pts with lung cancer, we hypothesize that PTX and PMB will have efficacy in pts with R/M SGC and that the combination will have improved anti-cancer activity compared with historical controls. Correlative studies on archived tissues include methylthioadenosine phosphorylase loss, PDL1 expression, and thymidylate synthase expression as potential biomarkers of response. Methods: MC200708 is a single institution (3-site), open-label, single arm phase II study of PTX and PMB in patients with R/M SGC. Pts will be treated in two cohorts: one for pts with adenoid cystic carcinoma (ACC) and the other for pts with all other types of SGC (non-ACC cohort). Eligible pts must be ≥18 years old, have a pathologically confirmed SGC that is not amenable to curative-intent therapy, ECOG 0-2, adequate organ function, and at least 1 measurable lesion by RECIST 1.1. Any number of lines of prior therapy is allowed; prior treatment with checkpoint inhibitors and/or PTX is allowed. Key exclusion criteria: serious medical co-morbidity or autoimmune disease, prior grade 3-4 adverse event (AE) or grade 2-4 lung AE with ICI, and uncontrolled brain metastases. Simon’s two-stage design will be used for each cohort separately given the expected difference in responses in pts with ACC and non-ACC. Primary endpoint is overall response rate. Secondary endpoints are progression free and overall survival and toxicity. All patients will receive the same treatment of PTX 500 mg/m2 IV + PMB 200 mg IV every 3 weeks until disease progression or treatment intolerance. Response assessments will occur every 3 cycles. Enrollment began July 2021 and 16 of the planned 45 patients (ACC cohort 9 of 20 pts, non-ACC 7 of 25) have been accrued. Clinical trial information: NCT04895735.