Although it mediates downstream signalling by inducing serine/threonine kinase activity, rather than by activating a tyrosine kinase receptor, transforming growth factor β (TGF-β) plays a role in tumour progression.58,59 Blocking TGF-β and its receptors decreased the tumour size and prevented metastasis in breast cancer and glioblastoma models and significantly improved the intratumoural penetration of low-molecular weight chemotherapy drugs and nanoparticles in breast cancer models. Here, NTRK1 is linked to breast cancer.