Sequential 10 μm frozen sections cut from a fresh-frozen AsPC-1 tumor were incubated in binding buffer (0.1%BSA, 40 mg/L bacitracin in PBS, pH 7.4) containing 0.5–10 nM 89Zr-MEHD7945A for 1 h at room temperature in a humidified chamber. Non-specific binding was assessed on additional sections by the addition of 100-fold mole excess of cold MEHD7945A. Activity standards of each concentration with a known volume were spotted onto a flexible TLC sheet (Avantor Performance Materials, Center Valley, PA). Sections and standards were then exposed to a storage phosphor plate, and read as described above. Activity concentrations of whole tumor section areas and standards were determined using ImageQuant 7.0 software, and subsequently converted to a molar concentration using the tumor sectional area calculated from the image, multiplied by the 10 µm section thickness to determine volume. Binding parameters (Bmax, KD) were determined by non-linear regression in addition to Scatchard analysis.