Prospective Observational Study On The Impact Of Early Response To First-line Anti-PD-1 Therapy In Patients With Recurrent And/Or Metastatic (R/M) Head And Neck Squamous Cell Carcinoma, Assessed By 18F-FDG PET/CT

Eligible patients will receive two administrations of Pembrolizumab as monotherapy.

An 18F-FDG PET/CT scan will be performed at baseline (T0; no more than 30 days before the first drug administration) and after two cycles (T1, at 6 weeks).

Patients will be considered responders if they achieve a complete response (defined as complete resolution of FDG uptake within the target lesions) or a partial response (i.e., >=30% decrease in the target tumor FDG SULpeak).

After the first two administrations of Pembrolizumab, as well as in case of progressive disease (i.e., >=30% increase in the target tumor FDG SULpeak or advent of new 18FDG-avid lesions), any treatment modification will be determined by the physician according to routine clinical practice