The main purpose of this first-in-human study of GEN1056, is to evaluate safety. In addition, the study will determine the recommended dose and frequency for subsequent clinical studies and will assess the preliminary anti-tumor activity of GEN1056. GEN1056 will be studied in patients with advanced or metastatic solid cancer, for whom standard of care (SOC) therapy is not an option. All participants will get GEN1056.

The trial is a first-in-human open-label, dose-finding, multinational safety trial, in participants with advanced or metastatic solid (non central nervous system [CNS]) tumors that have exhausted SOC therapy or are not candidates for SOC therapy, evaluating the safety, tolerability, preliminary antitumor activity, pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of GEN1056.

The trial will be conducted as follows:

• The Dose Escalation part (Part 1) will explore the safety of escalating doses of GEN1056
• The Dose schedule optimization part (Part 2) will explore further safety and tolerability in an alternate schedule of a dose based on data outcome available from Part 1.

Key Inclusion Criteria:

• Subjects with histologically or cytologically confirmed non-CNS advanced or metastatic solid tumors which has progressed despite standard therapy, or subjects who are intolerant of standard therapy, or for which no standard therapy exists, and for whom, in the opinion of the investigator, experimental therapy with GEN1056 may be beneficial
• Have personally (or in countries where permitted, their legally acceptable representative) signed an Informed Consent Form (ICF)
• Are at least 18 years of age.
• Have measurable disease according to the RECIST v1.1 criteria.
• Have an ECOG PS of 0 to 1 at screening and on C1D1 pre-treatment.
• Have acceptable laboratory test results during the screening period.
• Must provide an archival (FFPE) tumor tissue sample or newly obtained core or excisional biopsy of a tumor lesion not previously irradiated.
• A female subject with reproductive potential must agree to use adequate contraception during the trial, and for 4 months after receiving the last dose of trial drug GEN1056.

Key Exclusion Criteria:

• Subject is considered a poor medical risk due to a serious, uncontrolled inter-current illness

• Prior therapy with a checkpoint inhibitor agent or with an agent directed to another stimulatory or co-inhibitory T-cell receptor.

• Prior exposure to any of the following prior therapies within the specified timeframes:

  1. Systemic cytotoxic chemotherapy or antineoplastic biological therapy within 28 days or at least 5 elimination half-lives of the drug (whichever is shorter) of the first dose of trial treatment
  2. Radiotherapy within 21 days of start of trial treatment. Note: palliative radiotherapy be allowed.
  3. Prior treatment with live, attenuated vaccines within 28 days prior to initiation of GEN1056

• Known active CNS metastases and/or carcinomatous meningitis, or spinal cord compression.

• Positive for Human Immunodeficiency Virus (HIV), Hepatitis B (Hepatitis B Surface Antigen (HBsAg), HBV DNA), or Hepatitis C infection (Hepatitis C Virus Ribonucleic Acid (HCV RNA), HCV antibodies).

• An active, known, or suspected autoimmune disease, requiring systemic steroid.

• A condition requiring systemic treatment with either corticosteroids (>10 mg daily prednisone equivalent) or other immunosuppressive medications within 14 days of first treatment.

• History of non-infectious pneumonitis/interstitial lung disease that required steroids or has current pneumonitis/interstitial lung disease requiring treatment with steroids.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.