Hepatoblastoma (HB), the most common liver cancer in children, has become the fastest growing pediatric cancer in the United States. The extent of tumor resection remains the most significant prognostic factor for HB, leaving children with unresectable HB limited treatment options and a largely stagnant survival rate below 40%. Due to the rareness and heterogeneity of this pediatric solid tumor, clinically-relevant, patient-derived models are in urgent need in order to develop more effective therapy for individual patients. Recent studies on many adult cancers have proven patient-derived organoids (PDOs) are faithful in vitro models mimicking disease biology and patient drug response. Via the support from a 2017 NCCN Young Investigator Award, our lab tested HB organoid culture using a large cohort of patient-derived xenografts (PDXs). To date, we have grown HB PDOs from PDXs derived from primary, metastatic, and recurrent tumors at 82% (11/14), 100% (7/7), and 100% (2/2) successful rate, respectively. These HB PDOs displayed histopathology consistent with that of their parental tumors. When we tested the first group of 6 PDO lines to the 10 drugs included in recently opened COG AHEP1531 clinical trial for pediatric liver cancer, we found 2 lines whose parental tumors did not respond to HB standard-of-care cisplatin. They showed the same resistance to cisplatin as well as 2 other platinum-based drugs, carboplatin and oxaliplatin. PDOs derived from 2 matched primary and metastatic tumors showed most similar overall response. These results provided encouraging evidence supporting the notion that HB PDOs mimic patient drug response. Intriguingly, in a subset of cisplatin-resistant HB PDOs, vincristine and gemcitabine showed strong antitumor activities, which we will further validate in vivo using a novel neonatal liver xenograft model developed in our lab. To accurately model the unique early developmental tumor microenvironment (TME) of HB, we have successfully engrafted HB cells into the liver of postnatal day 5–7 mice. We found TME of the neonatal liver, indeed, has a strong and unique metastasis-promoting effect compared to that of the adult liver. With this first PDO effort on pediatric HB and our exciting preliminary data, we are confident that we are approaching our long-term goal of building an integrated “HB PDO Clinic” to enable accurate evaluation of disease risk and therapeutic response to facilitate personalized HB patient care.