A Phase I trial of MRTX1719, a PRMT5 inhibitor, has led to RECIST partial responses in MTAP-loss mesothelioma, non-small cell lung cancer, melanoma, gallbladder adenocarcinoma, and malignant peripheral nerve sheath tumor.19 Notably, the early efficacy signal in gallbladder adenocarcinoma, which is frequently an aggressive cancer and resistant to therapies, raises great excitement and interest in investigating MTAP-loss for GI cancers. This evidence concerns the gene MTAP and mesothelioma.