NTRK1 and cancer: Here, we for the first time demonstrate SM development by activation of TRKA in vivo , although the number of analyzed mice was limited, and present a new example that cancer cells can develop resistance to the therapeutic inhibition of receptor tyrosine kinase signaling by ligand-mediated receptor activation [32], which provide a means for cancer cells to re-establish the signaling pathways (e.g. MAPK in this study) that were present before the inhibitor therapy.