An activation of mTOR was seen in kaposiform lymphangiomatosis and kaposiform hemangioendothelioma but not in LM, whereas the activation of the ribosomal protein S6 kinase 1 (S6K1, an indicator of activated mTOR signaling), and the eukaryotic translation initiation factor 4E‐binding protein (4EBP1) which mediate an increase in protein synthesis and cell growth in lymphangiogenesis was seen in all cases of kaposiform lymphangiomatosis and kaposiform hemangioendothelioma and 40% of LM. Here, RPS6KB1 is linked to kaposiform hemangioendothelioma.