A phase II trial of pembrolizumab and cabozantinib in patients (pts) with recurrent metastatic head and neck squamous cell carcinoma (RMHNSCC).

6008 Background: Pembrolizumab (pembro) is an immune checkpoint inhibitor (ICI) approved for treating pts with recurrent/metastatic (RM) HNSCC. Cabozantinib (cabo) is a multiple receptor tyrosine kinase inhibitor (TKI) targeting MET and VEGFR2 shown to reduce tumor growth, metastasis, and angiogenesis and has immuno-modulatory properties. Methods: This is a phase II, open label multi-center, single arm trial evaluating the tolerability and clinical benefit of pembro administered at 200 mg every 3 weeks and cabo 40 mg daily for pts with RM HNSCC who have not received prior ICI. It had a lead-in safety cohort allowing reduction of cabo dose to 20mg daily. Eligible pts had RM HNSCC, deemed incurable, with a tumor PD-L1 CPS > 1, RECIST 1.1 measurable disease, a life expectancy of > 3 months, an Eastern Cooperative Group (ECOG) Performance Status (PS) of 0-1. Enrollment was initiated in March of 2019. We estimated that the ORR will improve to 35% with pembro+ cabo (from a historic of 18%) with a significance level of 0.05 and 80% power. Results: A total of 47 pts were screened, 13 screen failures [cavitation on scan (4), inability to swallow pills (2), other exclusions (7)]; 34 pts were enrolled, 32 were dosed and 31 evaluable (at least one follow-up scan). Pts had cancers of the oropharynx (21, 65%), nasopharynx (6, 19%), larynx/hypopharynx (4, 13%) and oral cavity (1,3%). 32 patients received cabo at 40 mg daily; 13 patients (41%) were dose reduced to 20mg daily [mucositis, increased liver function (LFT) tests, diarrhea]; males (n=29, 90%), median age 63 years (range 53-67); presence of distant metastases (34, 100%); prior radiation (29, 90%), chemotherapy (14, 43%); ECOG PS =0 (16, 50%), 1 (16,50%); HPV/p16 positive (17, 53%), negative (5, 16%), not applicable (10, 29%); the most frequent adverse event (AE) (all grades) was fatigue (16,50.0%), grade 3 or 4 treatment-related AE were increased LFTs, hyponatremia (3, 9.3% each). With a median follow up of 12.7 months (mos) (range 6.9- 20.5 mos), a RECIST 1.1 overall response rate ORR= 45.2% (CR=0; PR=14, 45.2%; SD =14, 45.2%; PD=3.0, 10%) with an overall clinical benefit of 90.4% were observed; The 1-yr OS was 67.7% (95% CI, 42.9%-83.6%; median 22.3 mos) and 1-yr PFS was 51.8% (95% CI, 28.8%-70.7%; median 14.6 mos). Conclusions: This phase II trial of pembro + cabo met its primary endpoint of ORR. The regimen is well-tolerated with very encouraging clinical activity in RM HNSCC and warrants further exploration in this disease. The study was supported by a grant from Exelixis to NFS. Clinical trial information: NCT03468218.