CD99 and Ewing sarcoma: Deregulation of macropinocytosis in cancer cells correlates with oncogenic RAS, as RAS-dependent signaling pathways hyperstimulate macropinocytosis in glioblastoma [4], and CD99 triggering induces methuosis of Ewing sarcoma cells through the insulin-like growth factor type 1 receptor (IGF-1R)/RAS/Rac1 signalling [15].