The urokinase-type plasminogen activator (uPA) is a serine protease that mediates its activity through a receptor (uPAR) and has an important role in several physiological processes such as matrix remodeling, inflammation, fibrinolysis, and cancer tumor angiogenesis, invasion, and metastasis (1). In addition, uPA activity is modulated by two specific inhibitors known as uPAI-1 and uPAI-2. The structure and functioning of uPA and its receptor is discussed in detail by Ploug (2). The uPA, uPAR, and the two inhibitors comprise the uPA system (uPAS), and any one or a combination of the uPAS components is known to be overexpressed in various malignant tumors, indicating a strong correlation of uPAS component overexpression to a poor prognostic outcome for the cancer patient (3). Therefore, investigators are interested in developing and evaluating agents that can be used non-invasively for the detection (e.g., by imaging techniques) and therapy (e.g., by radiotherapy with nuclide-containing uPAR ligands) of cancers that overexpress components of the uPAS. Li et al. recently reported the use of a linear, high-affinity uPAR antagonist, 64Cu-labeled peptide for the visualization of uPAR expression under preclinical conditions (4). In another study, Knor et al. evaluated and successfully used an α-emitting nuclide-conjugated peptide targeting the uPAR for the therapy of advanced ovarian cancer tumors in a mouse model (5). In a continued effort to develop and evaluate possible imaging agents for the visualization uPAR-expressing cancers, Liu et al. (6) synthesized and characterized a 111In-labeled (NAc-dD-CHA-F-dS-dR-Y-L-W-S-βAla)2-K-K(DOTA) peptide ([111In]anti-uPAR peptide; referred to as Test peptide from here on) under in vitro conditions and in mice bearing human breast cancer cell xenograft tumors.