NRG1 and osteosarcoma: Based on the NicheNet data and transcriptional data shown in the dot plot (Fig. 3), we chose to further investigate the effects of AREG, EGF, EREG, HBEGF, NRG1, TGFα, FGF2, FGF7, FGF10, FGF18, HGF, IGF-1, PDGF-AA, PDGF-BB, PDGF-CC, TGFβ1, and VEGFα on osteosarcoma cells in vitro alone or in combination with the highly selective MEK inhibitor (MEKi) PD0325901.