To investigate the safety and efficacy of sirolimus through the change in platelet counts during the sirolimus therapy on Kasaback-Merritt phenomenon(KMP).

Four patients were treated in Nanjing Children Hospital between Jaunary 2017 and June 2019 were enrolled in the study, including two males and two females. Their age was ranged from two days to three months. They all presented with huge mass located in neck or retroperitoneal and thrombocytopenia, hypofibrinogenemia. Their coagulation could not be improved by surgery or palate transfusion or steroids. They were all diagnosed as Kaposiform hemangioendothelioma(KHE) with KMP according to the biopsy, coagulation index and CT. Sirolimus were administered with 0.1 mg^-1·kg^-1·d^-1 or 0.8 mg/m², twice daily. Subsequent dose was adjusted to maintain the trough level between 10-15 ng/ml.Steroids were weaned gradually. Blood accounts were measured following the sirolimus administration.

All the four patients got improvement in platelet counts. Three patients went through a significant decreasing of palate counts after adding sirolimus for about 1-4 days. Two lesions prompted improvement with smaller size, lighter color and softer texture without complete regression. Two patients had elevated liver enzymes and/or interstitial pneumonia. One recovered while the other died of severe pneumonia with dyspnea. All the palate counts of survived patients remained in normal level in the following one year.

Sirolimus is an effective method in treating KMP and stabilizing platelet counts. However, it can not cure hemangioendothelioma.

Sirolimus; Kasabach-Merritt syndrome; Platelet count; Treatment outcome