ALX2004 for Advanced Solid Tumors

Inclusion Criteria: * Participants with locally advanced, recurrent or metastatic histologically confirmed HNSCC, NSCLC, ESCC, CRC; locally advanced or recurrent disease must not be amenable to resection with curative intent 1. Dose Escalation: Participants who have relapsed or progressed following prior anticancer therapy in the advanced/metastatic setting and for whom no approved or standard therapy is available. 2. Dose Exploration and Dose Expansion: The following tumor-specific criteria also apply. These cohorts will include all or a subset of these tumors. HNSCC - Received no more than 3 prior lines of therapy in the advanced or metastatic setting NSCLC - For participants with a targetable molecular alteration: received appropriate standard targeted therapy and no more than 2 prior lines of systemic chemotherapy in the advanced/metastatic setting. For participants without a targetable molecular alteration: received platinum-based chemotherapy and CPI (in combination or separately), and have received no more than 2 prior lines of systemic chemotherapy in the advanced/metastatic setting ESCC - Received no more than 3 prior lines of therapy in the advanced/metastatic setting CRC - For participants with a targetable molecular alteration (including dMMR or MSI-H): Received appropriate standard therapy for the alteration, at least 2 prior lines of systemic chemotherapy, and no more than 4 prior lines of therapy in the advanced/metastatic setting. For participants without a targetable molecule alteration: Received at least 2 prior lines of systemic chemotherapy (including an oxaliplatin-based chemotherapy), vascular endothelial growth factor (VEGF)-based therapy, and no more than 4 prior lines of therapy in the advanced/metastatic setting. * Adequate Bone Marrow Function * Adequate Renal \& Liver Function * Adequate Performance Status Exclusion Criteria: * Participants with disease suitable for local therapy with curative intent. * Has a life expectancy of less than 3 months and/or has rapidly progressing disease (e.g., tumor bleeding, uncontrolled tumor pain) in the opinion of the treating investigator * Prior treatment with any ADCs that have an active TOP1 inhibitor-based component