A Phase 1b/2, Open-label Study of Amivantamab Monotherapy and Amivantamab in Addition to Standard of Care Therapeutic Agents in Participants With Recurrent/Metastatic Head and Neck Squamous Cell Carcinoma

Inclusion Criteria:

• Have histologically or cytologically confirmed recurrent/metastatic head and neck squamous cell carcinoma (R/M HNSCC) that is considered incurable by local therapies. Acceptable prior lines of therapy will be determined according to specific cohort: (a) The eligible primary tumor locations are the oropharynx, oral cavity, hypopharynx, or larynx; (b) Any known p16 status of tumor must be negative (Note: All participants with an oropharyngeal tumor must have results of p16 status, per local testing); (c) Participants must provide local testing results of programmed cell death ligand 1 (PD-L1) status, if available
• Participants in Cohorts 1, 2, and 3B must have measurable disease according to RECIST version 1.1. Participants in Cohort 3A must have evaluable disease (defined as having at least 1 non-target lesion according to RECIST version 1.1
• Toxicities from previous anticancer therapies should have resolved to baseline levels or to Grade 1 or less prior to the first dose of study treatment (except for alopecia or post-radiation skin changes [any grade], Grade less than or equal to [<=]2 peripheral neuropathy and Grade <=2 hypothyroidism stable on hormone replacement)
• Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1
• Participant must have adequate organ and bone marrow function as follows, without history of red blood cell transfusion, platelet transfusion, or use of granulocyte colony-stimulating factor within 7 days prior to the date of the laboratory test.

Participants should have: a) Hemoglobin >=9 grams per deciliter (g/dL); b) Neutrophils >=1.5 x 10^3/mcg; c) Platelets >=100 x 10^3/mcg

Exclusion Criteria:

• Uncontrolled illness including any medical history or current (non-infectious) interstitial lung disease (ILD)/ pneumonitis/ pulmonary fibrosis, or where suspected ILD/pneumonitis/pulmonary fibrosis cannot be ruled out by imaging at screening
• Participant with untreated brain metastases leptomeningeal disease, or spinal cord compression not definitively treated with surgery or radiation
• Participant with a history of clinically significant cardiovascular disease
• Received prior chemotherapy, targeted cancer therapy, immunotherapy, or treatment with an investigational anticancer agent within 2 weeks or 4 half-lives, whichever is longer, before the first administration of study treatment. The maximum required washout is 28 days
• Received radiotherapy for palliative purposes within 7 days of the first administration of study treatment