IKS04 Regimen in Advanced Solid Tumors That Express CA242

Key Inclusion Criteria: * Advanced or metastatic CRC, BTCs, GEA, and PDAC that is histologically or cytologically confirmed * Disease that has progressed despite prior treatment, for which additional effective therapy is not available, not tolerable, is contraindicated, or the participant refuses standard therapy. * Platelets ≥ 100,000 /mcL * Hemoglobin ≥ 9.0 g/dL., no transfusions with RBCs are allowed within 2 weeks prior to first trial drug administration * ANC ≥ 1500/mcL * Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase \[SGOT\])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) ≤ 3 x institutional upper limit of normal (ULN) ≤ 5 x ULN if liver metastases present * Total bilirubin ≤ 1.5 x ULN, unless participant has Gilbert's Syndrome * Albumin \> 2.5 g/dL * Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1 Part I * Fresh biopsy tissue or formalin-fixed paraffin-embedded (FFPE) tumor tissue block or slides available for retrospective assessment of CA242 positivity in a central laboratory. * Measurable and non-measurable disease Part II * Fresh biopsy tissue or FFPE tumor tissue block or slides for assessment of CA242 positivity in a central laboratory prior to administration of first dose of study drug. * Measurable disease only Key Exclusion Criteria: * Participants with a significant pulmonary disease or condition, including: * Significant symptomatic chronic obstructive pulmonary disease (COPD), as assessed by the Investigator. * History or any current evidence on imaging studies of interstitial lung disease (ILD), pulmonary fibrosis. * History of pulmonary inflammatory disease, pneumonitis, acute respiratory distress syndrome (ARDS). * History of pneumonia within 3 months prior to the first trial drug administration. * Participants who have received previous treatment with any CA242 directed ADC or any ADC containing a PBD payload for their current tumor indication. * Participant may not have received more than 5 prior lines of systemic therapy. * Received treatment with a strong cytochrome P450 (CYP) 3A4 inhibitor within 7 days or 5 half-lives (whichever is longer) prior to the first trial drug administration * Central nervous system metastatic disease unless treated prior to first dose of trial drug. * Active second malignancy or history of another malignancy within the last 2 years with specific exceptions as per protocol * Active, known or suspected autoimmune disease, or a documented history of autoimmune disease or syndrome requiring systemic steroids or other immunosuppressive medications, such as: * Myocarditis, pneumonitis, glomerulonephritis. * Autoimmune hepatitis, inflammatory bowel disease (IBD) * Sjogren's syndrome * Rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) * Myositis * Myasthenia gravis * Guillain-Barré Syndrome * Multiple sclerosis * Granulomatosis with polyangiitis (Wegner's granulomatosis) * Vasculitis