In Phase IIa, dose-escalation study to determine the optimum tolerated dose and a recommended Phase IIb (RPIIb) dose in combination with pembrolizumab in subjects with recurrent or metastatic squamous cell carcinoma of the head and neck who have failed platinum or a platinum containing regimen.

In Phase IIb, randomized control study between NC-6004 in combination with pembrolizumab versus pembrolizumab alone in the same subject population as Part 1 at the RPIIb dose identified in PIIa.

Inclusion Criteria:

• Be willing and able to provide written informed consent for the trial.
• Males or females aged ≥18 years at screening.
• Have an Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.
• Have histologically- or cytologically-confirmed HNSCC.
• Have recurrent disease not amenable to curative treatment with local or systemic therapy, or metastatic (disseminated) HNSCC of the oral cavity, oropharynx, hypopharynx, or larynx that is considered incurable by local therapies.
• Having prior platinum failure.

Exclusion Criteria:

• Subjects with carcinoma of the nasopharynx, squamous cell carcinoma of unknown primary origination, squamous cell carcinoma that originates from the skin and salivary gland or paranasal sinus, nonsquamous histologies.
• Have disease that is suitable for locoregional treatment administered with curative intent or refuses curative intent.
• Have no more than 15% body weight loss due to the underlying condition in the last 3 months from signing of informed consent in Part 1 of the study and from randomization in to Part 2.
• Are currently participating in or have participated in a study of an investigational agent or are using an investigational device within 4 weeks prior to the first dose of trial treatment.
• Were previously treated with 3 or more lines of systemic therapies administered for recurrent and/or metastatic disease.