Main Inclusion Criteria:

   1. Age ≥ 18 years

   2. Histologically or cytologically-confirmed, HPV (+) or HPV (-) squamous cell carcinoma
   of the nasopharynx (WHO Type 1), oropharynx, hypopharynx, larynx (supraglottis,
   glottis, subglottis) or oral cavity.

   3. Recurrent or metastatic disease, documented by imaging (CT scan, MRI, X-ray) and/or
   physical examination with measurable disease as per Response Evaluation Criteria in
   Solid Tumors [RECIST] 1.1

For phase II cohorts:

   - Cohort #1: Patients who received a maximum of two prior systemic regimens for
   recurrent and/or metastatic disease and not amenable to further therapy with curative
   intent

   - Cohort #2: Patients with R/M SCCHN not amenable to therapy of curative intent, who
   have received a maximum of two prior systemic regimens in the R/M setting and who have
   received prior PD-(L)1 blockers

   - Cohort #3: Patients with R/M SCCHN who have not received prior systemic regimens in
   the R/M setting and who have not received prior PD-(L)1 inhibitors

Main Exclusion Criteria:

   1. For phase II cohort #1 and cohort #2: Patients who received more than 2 prior systemic
   regimens for recurrent and/or metastatic disease (no restriction in the phase Ib part
   of the trial).

   2. For phase II cohort #1 and cohort #2: Patients who received cetuximab or another
   inhibitor of epidermal growth factor receptor are excluded from the phase II of the
   trial, except if cetuximab was given as part of a primary treatment approach, with no
   progressive disease for at least 4 months following the end of prior cetuximab
   treatment.