Dr. Arun is one of the senior solid tumor faculty at UCSF, having joined the institution in 2019. His scholarly and clinical practice has focused on the treatment of pediatric liver cancers and rare cancers. He was the US National PI for the International Hepatoblastoma therapeutic trials, SIOPEL 4 and SIOPEL 6. He is currently the senior sub-PI for the Hepatocellular Carcinoma treatment arm of the Pediatric Hepatic tumors International Therapeutic Trial (PHITT). He is also the Co-chair of the Children's Hepatic tumors International Collaboration (CHIC), the largest extant database for pediatric rare tumors.

Dr. Arun facilitates an International Hepatobiliary Multicenter Tumor Board, where they consider therapeutic strategies for children with relapsed and refractory liver cancers from around the world, with expert participants from North America, Europe, and Asia.