Inclusion Criteria:  Histological or cytological evidence of relapsed or refractory solid tumor malignancy for which no standard therapy is available or standard therapy has failed Measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 as assessed by local site Investigator/radiology. Lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions Part 2 only, patients must have progressed per Investigator assessment on pembrolizumab or nivolumab, and agree and are able to continue on the inhibitor(s) while on study No other medical, surgical, or psychiatric condition (including active substance abuse) that would interfere with compliance to the protocol, as determined by the Principal Investigator  Exclusion Criteria:  Concurrent invasive malignancy Brain and/or leptomeningeal metastases, untreated or require current therapy Prior radiotherapy within 2 weeks of start of study treatment