We have been developing several new peptides and their radiolabeling methods for PET imaging of inflammation and cancer, targeting different types of biological targets (Käkelä et al. 2018; Li et al. 2013). Recently, using an in vivo phage display technique, Laakkonen and co-workers identified a brain tumor-homing peptide (named ACooP, sequence H-ACGLSGLGVA-NH2) that targets the fatty acid binding protein 3 (FABP3, also known as mammary-derived growth inhibitor or heart-type fatty acid-binding protein) (Hyvönen et al. 2014). The gene discussed is FABP3; the disease is brain neoplasm.