PDCD1 and squamous cell carcinoma: Epacadostat plus the PD-1 inhibitor nivolumab is being assessed in patients with advanced solid tumors, including NSCLC, in the phase I/II ECHO-204 study; promising preliminary antitumor activity has been reported, particularly in squamous cell carcinoma of the head and neck with epacadostat 300 mg BID in combination with nivolumab and in melanoma with epacadostat 100 mg BID or 300 mg BID in combination with nivolumab [24].