Inclusion criteria

• Tumor type:

1. Participants in Part A (dose escalation) and Part B (dose optimization) must have histologically- or cytologically-confirmed metastatic or unresectable solid tumor malignancy. Participants must have relapsed, refractory, or progressive disease, and should have no appropriate standard therapy available at the time of enrollment in the judgement of the investigator. Participants in Part A must have one of the following tumor types: * Colorectal cancer (CRC) * Gastric carcinoma (GC) (including signet-ring cell histology) and gastroesophageal junction adenocarcinoma (GEJ) * Non-small cell lung cancer (NSCLC), squamous or non-squamous histology * Pancreatic ductal adenocarcinoma (PDAC) * The tumor types to be enrolled in Part B will be identified by the sponsor from among those specified in Part A (dose escalation). 2. Part C (dose expansion): * Participants must have histologically- or cytologically-confirmed metastatic or unresectable solid tumor malignancy. * CRC * Prior therapy: Participants must have received prior treatment (in 1 or more lines of therapy) containing fluoropyrimidine, oxaliplatin, and irinotecan. * PDAC * Prior therapy: Participants must have received 1 prior line of therapy and received no more than 3 prior lines of therapy in the advanced or metastatic setting. * GC/GEJ * Prior therapy: Participants must have received prior platinum and fluoropyrimidine-based chemotherapy. * NSCLC - non-squamous/squamous * Prior therapy: Participants must have received platinum-based therapy. If eligible and consistent with local standard of care must have received a PD-1/PD-L1 inhibitor. * In addition, Participants with tumor genomic mutations/alterations for which approved targeted therapies are available per local standard of care, must have received such therapies. * Small cell lung cancer (SCLC) * Prior therapy: Participants must have received platinum-based therapy for extensive-stage disease and no more than 3 prior lines of therapy. If eligible and consistent with local standard of care must have received a PD 1/PD-L1 inhibitor. * Participants enrolled in the following study parts should have a tumor site that is accessible for biopsy(ies) and agree to biopsy(ies) and/or submission of archival tissue 1. Dose optimization 2. Disease-specific expansion cohorts * An Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1 * Measurable disease per Response Evaluation in Solid Tumors (RECIST) v1.1 at baseline.