27P Single cell RNA sequencing (scRNAseq) analysis of peripheral immune cell populations from patients treated with anti-PD1 with recurrent and/or metastatic squamous cell carcinoma of the head and neck (R/M SCCHN)

enables the quantification of ctDNA for GNAQ Q209L, GNAQ Q209P and GNA11 Q209L mutations.Patients with at least 2 available samples and clinical data were included.Results: 576 samples from 72 patients with rare MUM were analyzed.37 patients had GNA11 Q209L, 19 e GNAQ Q209P, and 16 e GNAQ Q209L mutation.37 patients had baseline samples prior to first-line treatment, 27 of which had detectable levels of ctDNA.Out of 52 patients with baseline samples prior to any line of therapy, 40 had detectable levels.In the first line cohort, non-detectable baseline ctDNA was predictive of better PFS (p 0.02, and a hazard ratio of 0.28 with p 0.025) and OS (p 0.03, and a hazard ratio of 0.14 with p 0.058).Baseline ctDNA was also predictive for PFS and OS of non first-line therapies (p 0.03 and p 0.01).Conclusions: ctDNA levels have a significant predictive value for PFS and OS in metastatic uveal melanoma, treated with first or subsequent lines of therapy.It provides a non-invasive method to predict outcome.