Background: Thrombopoietin receptor agonists (TPO-RAs) have demonstrated efficacy in treating clinically significant thrombocytopenia, including chemotherapy-induced thrombocytopenia (CIT) in adults. However, data regarding their safety and efficacy in pediatric, adolescents, and young adult (AYA) patients with hematologic malignancies are limited. Methods: We retrospectively identified 15 pediatric and AYA patients aged 25 years or younger with hematologic malignancies treated with a TPO-RA at UCSF Benioff Children’s Hospitals between 2015 and 2023. Platelet counts and transfusion requirements were compared before and after TPO-RA therapy. Results: The median age at TPO-RA initiation was 16 years (range: 7-25 years). Nine patients (60%) had a history of bleeding or comorbidity that predisposed to severe bleeding risk. Eleven patients received romiplostim and four patients received eltrombopag. The median platelet count significantly increased from 24 x 10 9/L at baseline to 54 x 10 9/L after 3 weeks of any TPO-RA therapy (p =0.029). Monthly platelet transfusion requirements significantly decreased from a median of 15 to two units after TPO-RA therapy (p=0.007). Fourteen of the 15 patients (93%) achieved a sustained platelet count >50,000/µL within eight weeks, with a median time to response of 3 weeks. No TPO-RA-related adverse events were observed. Conclusion: TPO-RAs were effective in managing refractory thrombocytopenia in pediatric and young adult patients being treated for hematologic malignancies, with a favorable safety profile, even among patients with multiple comorbidities. These findings warrant further investigation through prospective clinical trials to confirm efficacy and establish clinical guidelines for this population.

Background: V enetoclax is frequently used as salvage treatment in pediatric, adolescent, and young adult (AYA) patients with advanced hematologic malignancies. However, more robust data are needed from real-world studies to guide the safe and appropriate use of venetoclax in this population. Procedure: We retrospectively reviewed the medical records of all patients diagnosed with hematologic malignancies less than 30 years of age treated with venetoclax outside of clinical trials at the University of California San Francisco (UCSF) Benioff Children’s Hospitals from 2016 to 2022. Results: We identified 13 patients (AML , n= 8, B-ALL, n= 3, MDS, n= 2) aged 4 months to 27 years. A median of 3 prior lines of therapy were given (range 0 to 5). All patients received venetoclax in combination with either a hypomethylating agent or conventional chemotherapy. Three (23%) patients achieved a complete remission (CR); 2 (15%) achieved a partial remission (PR); 3 (23%) had stable disease (SD), and 5 (42%) had progressive disease. Median survival and time to progression from venetoclax initiation was 9 months (range 2.5 to 52 months), and 3 months (range 2 weeks to 7.5 months), respectively. Five patients (38%) developed life-threatening infections while receiving venetoclax, including bacteremia due to atypical organisms, invasive pulmonary infections with Aspergillus, cytomegalovirus (CMV) viremia, skin infections, encephalitis with bacterial brain abscesses. Conclusions: Venetoclax in combination with hypomethylating agents or cytotoxic chemotherapy was effective in a subset of pediatric/AYA patients with advanced hematologic malignancies, but was frequently associated with severe atypical infections, particularly in combination with cytotoxic chemotherapy.