Background: TAPUR is a phase II basket study evaluating anti-tumor activity of commercially available targeted agents in pts with advanced cancers with genomic alterations. Results in a cohort of HNC pts with CDKN2A loss or mutation treated with P are reported. Methods: Eligible pts had advanced HNC, no standard treatment options, measurable disease, ECOG PS 0-2, and adequate organ function. Genomic testing was performed in CLIA-certified, CAP-accredited site selected labs. Pts received P at 125 mg orally once daily for 21 days, followed by 7 days off until disease progression. Pts matched to P had CDKN2A loss or mutation and no RBmutations. Simon 2-stage design tested the null disease control (DC) - defined as partial (PR), complete response (CR) or stable disease at 16+ weeks (SD 16+) - rate of 15% vs. 35% (power = 0.85; α = 0.10). If ≥2 of 10 pts in stage 1 have DC, 18 more pts are enrolled. If ≥7 of 28 pts have DC, the null DC rate is rejected. Secondary endpoints are progression-free survival (PFS), overall survival (OS) and safety. Results: 28 pts (64% male) with HNC with CDKN2Aloss (20 pts) or mutation (8 pts) were enrolled from June 2016 to Sept 2019. All were eligible for efficacy and toxicity. Demographics and outcomes are summarized in Table. No objective response (OR) and 10 pts with SD16+ (9 with CDKN2A loss, 1 with mutation) were observed for a DC rate of 37% (95% CI: 21%, 50%); the null DC rate of 15% was rejected (p=0.005). 14 pts had at least one grade 3-5 adverse or serious adverse event (AE/SAE) at least possibly related to P with the most common being low WBC/platelets. Other grade 3-4 AEs included anemia, fatigue, hypocalcemia, and syncope. There was one pt with grade 5 respiratory failure likely due to extensive lung metastases and aspiration but P-related pneumonitis could not be ruled out. Conclusions: Monotherapy P demonstrated modest anti-tumor activity and clinically significant AEs in heavily pre-treated pts with HNC with CDKN2Aloss or mutation. Additional study is warranted to confirm the efficacy of P in pts with HNC with CDKN2Aloss or mutation. Clinical trial information: NCT02693535