To assess potential predictors of efficacy of tebentafusp, changes in serum ctDNA levels were measured using a custom panel including mutations commonly found in uveal melanoma (GNAQ Q209L/P; GNA11 Q209L; SF3B1 K700E, R625L/H/C; PLCB4 D630N/Y/V; CYSLTR2 L129Q; and EIF1AX G15D) (Methods and Supplementary Table 4). The gene discussed is GNAQ; the disease is uveal melanoma.