Corticosteroid-to-sirolimus sequential therapy: a case series of infantile kaposiform hemangioendothelioma associated with Kasabach-Merritt phenomenon.

Background: Kaposiform hemangioendothelioma (KHE) with Kasabach-Merritt phenomenon (KMP) is a rare and life-threatening vascular tumor in infants, characterized by severe thrombocytopenia and consumptive coagulopathy. Although corticosteroids and sirolimus have both been used in treatment, there is no consensus on the optimal regimen, and evidence remains limited regarding sequential therapeutic strategies. This study aimed to explore the efficacy and safety of corticosteroid-to-sirolimus sequential therapy in a retrospective case series. Methods: From June 2022 to December 2024, nine infants diagnosed with KHE and KMP at our hospital received corticosteroid-to-sirolimus sequential therapy. Initial treatment included intravenous methylprednisolone (4 mg/kg/day), followed by a switch to oral methylprednisolone (4 mg/kg every other day) in combination with oral sirolimus (0.8 mg/m2 twice daily), with dose adjustments to maintain sirolimus blood concentrations between 10-15 ng/mL. Treatment efficacy was assessed by platelet recovery time, tumor regression (via imaging), and overall response rates according to modified RECIST criteria. Safety outcomes were evaluated by monitoring adverse events graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 2.0 (NCI-CTCAE v2.0.). Follow-up lasted 6 months to 2 years. Results: All patients achieved a platelet count ≥100×109/L within 3.0±1.7 days after corticosteroid initiation. Four patients experienced transient platelet declines during the combination phase, but all stabilized within 8.3±6.3 days. The combination therapy lasted 49.0±4.2 days, followed by sirolimus monotherapy for 4-23 months (mean 12.8±6.8 months). Adverse events were mostly mild to moderate and manageable, with no severe complications reported. Conclusions: Corticosteroid-to-sirolimus sequential therapy demonstrated favorable short-term efficacy and acceptable safety in this small series of infants with KHE and KMP. However, given the limited sample size and lack of long-term follow-up beyond two years, further prospective studies are necessary to validate these findings and assess potential late relapses or adverse effects.