EGFR and osteosarcoma: Application of EGF for 15 min to serum-starved osteosarcoma cells led in most cases to a distinct activation of EGFR phosphorylation and of the respective downstream MAPK (ERK phosphorylation) and PI3K/AKT (AKT, S6, and GSK3β phosphorylation) signaling pathways (Fig. 1b, densitometric quantification in Fig. 1c).