Duvelisib Plus Docetaxel In Recurrent/Metastatic HNSCC

Inclusion Criteria: * Participants must meet the following criteria on screening examination to be eligible to participate in the study: * Participants must have histologically confirmed squamous cell carcinoma of the head and neck (SCCHN) with evidence of recurrent, metastatic (R/M) or advanced, incurable disease from any mucosal subsite including oral cavity, oropharynx, larynx, hypopharynx, nasal cavity, and the paranasal sinuses. * Participants must have at least one RECIST v1.1 measurable lesion, as defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded for non-nodal lesions and short axis for nodal lesions) ≥1 cm with CT scans or MR imaging. * Must have had at least 1, but no more than 2, prior lines of prior systemic therapy for R/M SCCHN; one of these lines should have included PD-1/L1 blockade * Platinum-based therapy as part of definitive/adjuvant or curative-intent treatment can count as 1 prior line of therapy if the subject progressed within 6 months of receiving therapy. * At least 2 weeks must have elapsed since the end of prior chemotherapy, biological agents (3 weeks for anti-cancer monoclonal antibody containing regimens) or any investigational drug product, with adequate recovery of treatment-related toxicity to NCI CTCAE Version 5.0 grade ≤1 (or tolerable grade 2) or back to baseline (except for alopecia or peripheral neuropathy). * Be ≥18 years of age on the day of signing informed c…