Ligand binding to PlexinB1 results in activation of the receptor tyrosine kinases ErbB2 [9], EGFR [10], and Met [11] and drives invasiveness of prostate cancer cells [12,13] through regulation of several small GTPases, including Rho [14], R-Ras [15], and Rap [16]. The gene discussed is PLXNB1; the disease is prostate cancer.