Based on emerging preclinical data for enhancement of immune checkpoint blockade by arginine deprivation in urea cycle dysregulated cancers, and higher objective response rates in UM with dual immune checkpoint inhibition, a phase 1 study of ADI‐PEG20 with CTLA‐4 and PD‐1 combined immune checkpoint blockade has accrued in advanced UM (NCT03922880) for which results are awaited. This evidence concerns the gene CTLA4 and cancer.