Clinical Research Directory

Inclusion Criteria: All cohorts: * Be at least 18 years of age. * Have measurable disease according to RECIST v1.1. * Provide all pre-baseline scans since failure of last prior therapy (ie, documented radiographic progressive disease \[PD\]), if available. * Have Eastern Cooperative Oncology Group performance status (ECOG PS) score of 0 to 1 at screening and on C1D1 pretreatment. * Provide a biopsy (ie, formalin-fixed paraffin-embedded slides/block). A fresh biopsy taken during the screening period is preferred, unless medically unfeasible and after review and approval by the sponsor. If this cannot be provided, a biopsy taken after failure/stop of last prior treatment and taken within 6 months prior to C1D1 may be provided. Phase 1a and 1b- Dose Escalation: * Have histologically or cytologically confirmed non-Central Nervous System (CNS) primary solid tumors who have metastatic or advanced disease. * Have progressed on standard of care (SoC) therapy which should include platinum-based chemotherapy and anti-PD/PD-L1 therapies, if applicable for the tumor type, or for whom there is no available standard therapy likely to provide clinical benefit, and for whom experimental therapy with GEN1055 or GEN1055+pembrolizumab may be beneficial, in the opinion of the investigator. Phase 2a - Expansion: Inclusion criteria specific to selected tumor indications may apply. Exclusion Criteria: * Has uncontrolled intercurrent illness, including but not limited to: * Ongoing or active infection requiring IV treatment with anti-infective therapy administered less than 2 weeks prior to first dose (including coronavirus disease 2019 \[COVID-19\] infection). * Significant cardiovascular impairment including: i) Symptomatic congestive heart failure (Class III or IV as classified by the New York Heart Association), unstable angina pectoris, or cardiac arrhythmia. ii) Uncontrolled hypertension defined as systolic blood pressure ≥160-millimeter (mm) Hg and/or diastolic blood pressure ≥100 mm Hg, despite optimal medical management. iii) Prolonged corrected QT interval at baseline of ≥470 milliseconds using Fridericia's QT correction formula. * Ongoing or recent (within 1 year of screening) evidence of significant autoimmune disease that required treatment with systemic immunosuppressive treatments, which may suggest risk for immune-related adverse events (irAEs). * History of grade 3 or higher irAEs that led to treatment discontinuation of a checkpoint inhibitor (CPI). A participant with irAEs below grade 3 that led to discontinuation should be discussed with the sponsor. Grade 3 irAEs that have fully recovered may also be discussed. * History of chronic liver disease (eg, alcoholic hepatitis or nonalcoholic steatohepatitis), drug-related or autoimmune hepatitis, or evidence of hepatic cirrhosis. * Evidence of interstitial lung disease. * Ongoing pneumonitis (any grade) including any radiological change of ongoing pneumonitis at baseline or history of noninfectious drug-, immune-, or radiation-related pneumonitis that has required steroids. * Has been exposed to any of the following prior therapies/treatments within the specified timeframes: * Treatment with an anticancer agent within 4 weeks or for systemic therapies within 5 half-lives of the drug, whichever is shorter, prior to trial treatment administration. * Condition requiring systemic treatment with either corticosteroids (\>10 mg daily prednisone equivalent) or other immunosuppressive medications within 14 days of first treatment. Inhaled or topical steroids, and adrenal or pituitary replacement steroid \>10 mg daily prednisone equivalent, are permitted in the absence of active autoimmune disease. * Has received granulocyte or granulocyte/macrophage colony-stimulating factor support within 2 weeks prior to first trial treatment administration or is chronically transfusion-dependent. * RT within 14 days before the planned first dose of trial treatment. Palliative RT of bone metastases up to 7 days prior to C1D1 will be allowed. * Hepatitis (testing for hepatitis B or C is not required unless mandated by local health authority): * Hepatitis B virus (HBV): Has a medical history or positive serology for HBV (defined as positive for hepatitis B surface antigen or HBV deoxyribonucleic acid \[DNA\]). i) Above is not exclusionary if deemed due to vaccination, resolved natural infection, or passive immunization due to immunoglobulin therapy. * Hepatitis C virus (HCV): Known active HCV infection (defined as positive for HCV ribonucleic acid \[RNA\] \[qualitative\]). Note: Other protocol defined inclusion and exclusion criteria may apply.