A Study to Evaluate Safety, Tolerability, and Preliminary Effect of the GEN1053 Antibody on Malignant Solid Tumors as Monotherapy

Key Inclusion Criteria:

For both the Dose Escalation and Expansion parts:

* Be ≥18 years of age.
* Have measurable disease according to RECIST 1.1
* Provide all pre-baseline scans since failure of last prior therapy (ie radiographic PD), if available
* Have Eastern Cooperative Oncology Group performance status ≤1.
* Have organ and bone marrow function as follows:

Bone marrow / hematological function:

* Absolute neutrophil count (ANC) ≥1.5×10\^9/L
* Hemoglobin ≥9.0 g/dL
* Platelet count ≥150×10\^9/L

Liver function:

* Total bilirubin ≤ upper limit of normal (ULN)
* Alanine aminotransferase ≤1.5×ULN
* Aspartate aminotransferase ≤1.5×ULN
* Albumin ≥30 g/L

Coagulation status:

* Prothrombin time (PT)/International normalized ratio ≤1.5
* Activated partial thromboplastin time (aPTT) ≤1.5×ULN
* Renal function: Glomerular filtration rate ≥45 mL/min/1.73 m², according to the abbreviated Modification of Diet in Renal Disease equation

For Monotherapy Dose Escalation (phase 1) only:

* Subjects with histologically or cytologically confirmed non-CNS solid tumors that are metastatic or advanced.
* Subjects who have progressed on standard of care therapy or for whom there is no available standard therapy likely to provide clinical benefit, or who are not candidates for or refuse such available therapy, and for whom, in the opinion of the investigator, experimental therapy with GEN1053 may be beneficial.
* Fresh biopsies mandatory for all patients in Monotherapy Dose Escalation

For the Expansion part Only:

•Subjects with histologically or cytologically confirmed diagnosis of recurrent, unresectable or metastatic HNSCC, who have progressed on standard of care therapy or do not have any further available standard therapy or are not candidates for or refuse standard therapy (if subjects had access), and for whom experimental therapy with GEN1053 may be beneficial in the opinion of the investigator.

Key Exclusion Criteria (all parts):

* 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.
  * Symptomatic congestive heart failure (Grade III or IV as classified by the New York Heart Association), unstable angina pectoris or cardiac arrhythmia.
  * Uncontrolled hypertension defined as systolic blood pressure ≥160 mm Hg and/or diastolic blood pressure ≥100 mm Hg, despite optimal medical management.
  * Prolonged QTc interval at baseline of ≥470 milliseconds using Fridericia's QT correction formula.
  * Ongoing or recent (within 1 year) evidence of significant autoimmune disease that required treatment with systemic immunosuppressive treatments, which may suggest risk for irAEs.
  * History of grade 3 or higher irAEs that led to treatment discontinuation of a CPI.
  * History of chronic liver disease or evidence of hepatic cirrhosis.
  * Evidence of interstitial lung disease.
  * Ongoing pneumonitis or history of non-infectious pneumonitis that has required steroids.
  * Known platelet function defects
* Prior therapy:

  * Radiotherapy within 14 days prior to first GEN1053 administration. Palliative radiotherapy will be allowed.
  * Treatment with an anti-cancer agent (within 28 days or after at least 5 half-lives of the drug, whichever is shorter), prior to GEN1053 administration.
  * Subject with a 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.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply