ASS1 and mesothelioma: Approximately 50% of mesotheliomas do not express ASS1,4 making arginine depletion with pegylated arginine deiminase (ADI-PEG20) an attractive personalized therapeutic strategy3 that has shown significant activity in the randomized phase 2 Arginine Deiminase and Mesothelioma (ADAM) trial.5