A Study of AMG 355 Alone and in Combination With Pembrolizumab in Participants With Advanced Solid Tumors

Key Inclusion Criteria: * Age ≥ 18 years at the time of signing informed consent. * Participants with histologically or cytologically confirmed metastatic or locally advanced solid tumors who have relapsed after and/or are refractory to or ineligible for established and available therapies with known clinical benefit at time of pre-screening: * Group A: NSCLC, CRC, GC, and melanoma. * Group B: NSCLC, CRC, GC. * Eastern Cooperative Oncology Group Performance status 0 or 1. * Life expectancy of \> 3 months, in the opinion of the investigator. * At least 1 measurable lesion as defined by modified RECIST 1.1 guidelines. Note: this lesion should be avoided for the required biopsies on the study. * Participants must be willing to undergo 1 or more biopsies as follows: * Fresh biopsy prior to enrollment is preferred or, if fresh tissue is not obtainable, an archival tumor sample may be acceptable if the sample was obtained within 6 months of enrollment and participant has not received any other treatment since sample was obtained, consult the Medical Monitor. * Mandatory fresh biopsy during cycle 2 (before the restaging of CT-scan) of treatment with AMG 355 (± pembrolizumab). Note: Where slides are accepted, samples must consist of a minimum of 11 (21 preferred) freshly-cut, serially, sectioned, unstained slides. A formalin-fixed, paraffin embedded block is preferred if available, but in lieu of a block, unstained slides or fresh wet tissue is acceptable. Key Exclusion …