The demonstration that siRNA-mediated downregulation of the ABC transporter ABCC1 prevented LPI release and inhibited LPI-dependent cell signalling and proliferation led us to hypothesise that an autocrine loop exists by which prostate cancer cells release LPI via ABCC1 to sustain their proliferation through activation of GPR55 [12]. The gene discussed is ABCG2; the disease is prostate carcinoma.