Formulations of pegylated arginine deiminase

A lyophilized formulation, comprising arginine deiminase-polyethylene glycol 20K (ADI-PEG 20), wherein the lyophilized formulation is at a pharmaceutically-acceptable pH, a histidine buffer at a concentration of about 1 to about 50 mM, sodium chloride, and sucrose at about 1 wt % to about 20 wt %, and wherein the ADI-PEG 20 retains at least 85%, 90% or 95% arginine deiminase (ADI) activity relative to a corresponding ADI-PEG 20 in a non-lyophilized liquid control composition after being stored as a lyophilized formulation over 3 months at a temperature of 2-8° C.