PTK2 and cancer: In neurons, β1 increases neurite length via fyn kinase.15 CAM-mediated activation of fyn kinase is proposed to initiate the fyn-focal adhesion kinase (FAK) pathway, activating extracellular signal-regulated kinase 1/2, leading to neurite outgrowth.38 Fyn is upregulated in a number of cancers, where it contributes to an invasive phenotype.39 We found that fyn, like β1, was expressed in MCF-10A cells and BCa cell lines (Fig. 1g and 1h, Supporting Information Fig. S2f).