A single-arm phase II trial to assess the efficacy and safety profile of pembrolizumab in patients with performance status of 2 with recurrent or metastatic squamous cell carcinoma of the head and neck. Patients will receive best supportive care + pembrolizumab 200mg every 3 weeks for a maximum duration of 24 months

Inclusion Criteria:

1. Histologically confirmed locally advanced, recurrent or metastatic squamous cell carcinoma of the head and neck that is considered incurable by local therapies
2. Measurable disease evaluated by RECIST criteria version 1.1
3. WHO performance status of 2
4. Life expectancy >12 weeks
5. Aged ≥18 years of age
6. Adequate bone marrow function
7. Adequate renal function
8. Adequate liver function
9. Willing to use highly effective contraception for the duration of trial treatment and for 120 days after completion of treatment
10. Able to give informed consent, indicating that the patient has been informed of and understands the experimental nature of the study, possible risks and benefits, trial procedures, and alternative options
11. Willing and able to comply with the protocol for the duration of the study, including the treatment plan, investigations required and follow up visits

Exclusion Criteria:

1. Patients with undifferentiated nasopharyngeal or sino-nasal cancers
2. Disease suitable for treatment with curative intent
3. Prior therapy with an anti-PD-1, anti-PD-L1 or anti-PD-L2 agent
4. Any investigational agents within 4 weeks prior to registration
5. Anti-cancer monoclonal antibody therapy within 4 weeks prior to registration
6. Chemotherapy, targeted small molecule therapy, or radiotherapy within 2 weeks prior to registration
7. Patients with concurrent or previous malignancy that could compromise assessment of the primary or secondary endpoints of the trial
8. Women who are pregnant or breast feeding
9. Grade 3 or 4 peripheral neuropathy
10. Any serious and/or unstable pre-existing medical, psychiatric or other condition that, in the treating clinician's judgment, could interfere with patient safety or obtaining informed consent
11. Active central nervous system (CNS) metastases and/or carcinomatous meningitis
12. Active hepatitis B or C infection
13. Immunocompromised patients (e.g. known HIV positive status)
14. Prior organ transplantation including allogenic stem-cell transplantation
15. History of (non-infectious) pneumonitis/interstitial lung disease that required steroids, or current pneumonitis/interstitial lung disease
16. Active infection requiring systemic therapy
17. Received a live vaccine within 30 days prior to registration
18. Diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of trial treatment
19. Active autoimmune disease that might deteriorate when receiving an immune-stimulatory agent.
20. Current use of immunosuppressive medication (exceptions apply) Refer to section 7.2 for full list of eligibility criteria