To test whether arginine deprivation mediated by rhArg1peg5000 could impair tumor growth in vivo, we subcutaneously implanted ASS1-negative RKO cells and ASS1-positive SW480 cells into the hind flanks of immunocompromised athymic nude mice, which were then randomized to twice a week treatment schedule (0.5 mg of rhArg1peg5000 per animal) or vehicle control. Here, ASS1 is linked to neoplasm.