This is a Phase 1/2, open-label, non-randomized, 4-part trial to determine the safety profile and identify the maximum tolerated dose (MTD) and/or recommended Phase 2 dose (RP2D) of INBRX 106 administered as a single agent or in combination with the anti-PD-1 checkpoint inhibitor (CPI) pembrolizumab (Keytruda®). KEYTRUDA is a registered trademark of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA.

Select Inclusion Criteria:

• Males or females aged ≥18 years.
• Parts 1 and 3 (escalation cohorts): Subjects with locally advanced or metastatic non resectable solid tumors, whose disease has progressed despite all standard therapies or for whom no further standard or clinically acceptable therapy exists.
• Part 2 (single-agent expansion cohort): Subjects with NSCLC, melanoma, HNSCC, G/GEA, RCC, or TCC, with histologically confirmed, locally advanced or metastatic, non-resectable disease, which has progressed despite all standard therapies including CPI or for whom no standard or clinically acceptable therapy exists.
• Part 4 (expansion cohorts in combination with pembrolizumab, with or without chemotherapy): Subjects with melanoma (all types), HNSCC, G/GEA, RCC, TCC, NSCLC, or MSI-high, TMB-high, MMR-deficient tumors, with histologically confirmed, locally advanced or metastatic, non resectable disease, which is either CPI-naive (melanoma, HNSCC, NPC) or progressed despite all standard therapies including CPI (NSCLC, RCC, TCC, uveal melanoma, MSI-high, TMB-high, or MMR-deficient solid tumors) or for whom no standard or clinically acceptable therapy exists.
• For Cohort F3 (NSCLC), subjects may have progressed on no more than 2 lines of standard therapy that must include at least one PD-1/L1 regimen.
• For Cohort F4 (HNSCC and NPC), subjects may be previously treated with no more than 1 prior chemotherapy regimen in metastatic setting. Prior PD-1/L1 in curative (neo-adjuvant/adjuvant) setting is allowed only if completed >/= 6 months prior to progression to local recurrence or metastatic disease.
• All subjects with non-squamous NSCLC must have documentation of absence of tumor activating EGFR mutations and absence of ALK gene rearrangements.
• PD-L1 by IHC (22C3): Parts 1 and 3: IHC optional. Part 2: IHC result mandatory but any score allowed. Combined Positive Score (CPS) ≥ 1% (or Tumor Proportion Score ≥50% for NSCLC; for TMB-high tumors, any TPS% is allowed). Part 4: Combined Positive Score (CPS) ≥ 1% (or Tumor Proportion Score ≥50% for NSCLC; for TMB-high tumors, any TPS% is allowed).
• Adequate hematologic, coagulation, hepatic and renal function and ECOG score as defined per protocol.

Select Exclusion Criteria:

• Prior exposure to OX40 agonists.
• Receipt of any investigational product or any approved anticancer drug(s) or biological product(s) within 4 weeks prior to the first dose of study drug with certain exceptions.
• Hematologic malignancies (e.g., ALL, AML, MDS, CLL, CML, NHL, Hodgkin's lymphoma and multiple myeloma)
• Prior or concurrent malignancies. Exception: Subjects with a prior or concurrent malignancy whose natural history or treatment does not have the potential to interfere with the safety or efficacy assessments of INBRX-106.
• Known active central nervous system (CNS) metastases and/or carcinomatous meningitis. Exception: Subjects who are previously treated and are radiologically and clinically stable without the requirement for steroid treatment for at least 14 days prior to first dose of study treatment may be allowed study entry if certain criteria apply.
• Grade ≥ 3 immune-related adverse events (irAEs) or irAE that lead to discontinuation of prior immunotherapy. Some exceptions as defined per protocol apply.
• Active autoimmune disease or documented history of autoimmune disease that required systemic steroids or other immunosuppressive medications. Certain exceptions as defined in protocol apply.
• Diagnosis of immunodeficiency or treatment with systemic immunosuppressive medications within 7 days prior to the first dose of study drug. Certain exceptions as defined in protocol apply.
• History of hepatitis B, hepatitis C, or human immunodeficiency virus (HIV) infection. Exceptions as defined in protocol apply.
• Active interstitial lung disease (ILD) or pneumonitis or a history of ILD or pneumonitis requiring treatment with steroids or other immunosuppressive medications.
• Clinically significant cardiac condition, including myocardial infarction, uncontrolled angina, cerebrovascular accident, or other acute uncontrolled heart disease < 3 months; left ventricular ejection fraction (LVEF) < 50%; New York Heart Association (NYHA) Class III or IV congestive heart failure; or uncontrolled hypertension; or oxygen saturation <92% on room air.
• Active, hemodynamically significant pulmonary embolism within 3 months prior to enrollment on this trial.
• Major surgery within 4 weeks prior to enrollment on this trial.
• Anti-infectious drug treatments (i.e., antibiotics) within 4 weeks prior to the first dose of study drug.
• Prior organ allograft transplantations or allogeneic peripheral blood stem cell (PBSC) or bone marrow (BM) transplantation.
• Additional in- and exclusion criteria per protocol.

Part 4 NSCLC cohort is randomized 1;1:1, open-label