They can also be secreted by endothelial cells surrounding the tumor, as demonstrated by the increased levels of MMP2, NOS, and VEGF in endothelial cells following activation of signaling pathways such as PI3K and ERK downstream of NGF‐activated TrkA, leading to enhanced invasion, cord formation, and monolayer permeability in a breast cancer model (Romon et al, 2010). Here, NTRK1 is linked to neoplasm.