Interestingly, this outcome correlated with significant downregulation of the ASS1 gene in sarcomatoid compared with epithelioid MPM.29 One of our patients with biphasic MPM remains alive 26 months after presentation, with a debilitating corticosteroid-refractory anticyclic citrullinated peptide antibody-positive paraneoplastic arthritis of the hands, described previously with several cancers but not with MPM.30 The arthritis resolved within the first cycle of ADIPemCis and then fluctuated at a lower intensity while the patient was receiving ADI-PEG20 monotherapy. The gene discussed is ASS1; the disease is arthritic joint disease.