The study is comprised of 2 phases. Phase 1 (dose escalation) includes participants with solid tumors known to express New York esophageal squamous cell carcinoma 1 (NY-ESO-1). Phase 2 (ASP0739 as single agent and in combination with pembrolizumab) includes participants with relapsed/refractory Synovial Sarcoma (SS), myxoid/round cell liposarcoma (MRCL), and ovarian cancer who have not responded to Standard of Care (SOC) or are ineligible for standard therapy. Phase 2 single agent will also include a cohort of participants with select solid tumors known to express NY-ESO-1 (melanoma, Non Small Cell Lung Cancer-adenocarcinoma [NSCLC], squamous cell and esophageal squamous cell carcinoma [ESCC]). Japanese participants will only be enrolled into the monotherapy arm of the dose expansion cohort.
The purpose of this study is to evaluate the safety, and tolerability of ASP0739, when administered as a single agent and in combination with pembrolizumab.~This study will also evaluate the clinical response and other measures of anticancer activity of ASP0739 when administered as a single agent and in combination with pembrolizumab based on central and local assessment.