NTRK1 and cancer: For example, cancer cell growth is regulated by growth hormone receptors, whose amounts are controlled by endocytosis (Mellman and Yarden, 2013); activated receptor tyrosine kinases (RTK)-ligand complexes, e.g., EGFR-EGF, could activate its downstream targets, such as MEK–ERK pathway, to promote cell growth (Roberts and Der, 2007).