Inclusion Criteria:

          -  Patients must have histologically or cytopathologically confirmed diagnosis of
             non-cutaneous squamous cell carcinoma of the head and neck region that is locally
             advanced and/or recurrent and no longer amenable to local surgical or radiation
             therapy and/or with evidence of distant metastatic disease

          -  Patients must have had anti-PD-(L)1 therapy as the most recent systemic therapy with
             either stable disease or partial response on prior anti-PD-(L)1 therapy, or
             progressive disease on prior anti-PD-(L)1 therapy

          -  Patients must have disease that is measurable by RECIST v1.1

          -  Patients must be willing to provide tumor tissue biopsy

          -  Patients must demonstrate adequate organ function

          -  Female patients of childbearing potential should have a negative pregnancy test within
             72 hours prior to receiving the first dose of study medication

          -  Patients must agree to follow contraceptive requirements defined in the protocol

          -  Additional criteria apply

        Exclusion Criteria:

          -  Patient is pregnant or breastfeeding or expecting to conceive or father children

          -  Patient has an active major infection requiring systemic therapy within 1 week of
             starting study drug

          -  Patient has known active central nervous system (CNS) metastases and/or carcinomatous
             meningitis. Patients with previously treated brain metastases may participate,
             provided that they are stable, have no evidence of new or enlarging brain metastases,
             and are not using steroids for at least 7 days prior to study drug

          -  Patient has hypersensitivity to pembrolizumab, ALKS 4230, or any of their excipients

          -  Patient has a diagnosis of immunodeficiency or is receiving systemic steroid therapy
             (inhaled or topical steroids and steroid replacement at physiologic doses are
             allowable)

          -  Patient has prior Grade ≥3 immune-related toxicities requiring systemic
             immunosuppressant treatment that were attributable or possibly attributable to PD-1
             immune checkpoint blockade

          -  Patient has active tuberculosis or known active infection with hepatitis B or
             hepatitis C

          -  Patient has known psychiatric or substance abuse disorders or a social situation that
             would interfere with cooperation with the requirements of the study

          -  Additional criteria apply