89Zr-MEHD7945A [200–275 μCi (7.4–10.2 MBq), 44–61 µg, 290–400 pmol] in sterile saline was intravenously (i.v.) administered on the lateral tail-vein in mice (n = 3–4) bearing either BxPC-3 or AsPC-1 s.c. xenografts. Small-animal PET scans were acquired between 24–96 h post-tracer administration using microPET-R4 and/or Focus 120 scanners (Concorde Microsystems). The mice were fully anesthetized with 1–2% isoflurane (Baxter, Deerfield, IL) throughout the scan. Images were reconstructed via filter back projection. ASIPro VMTM software (Siemens Concorde Microsystems) was used to analyze volumes-of-interest (VOI) on various planar sections from the acquired image by manually drawing on the tumor site and on select organs. The average VOI was calculated and expressed as % injected dose per gram of tissue (%ID/g). To prove specificity, competitive inhibition studies were conducted by co-administering ~200–500 µg (1.33 nmol–3.33 nmol) of non-radioactive MEHD7945A in BxPC-3 tumor-bearing mice (n = 3–5). PET imaging with 89Zr-IgG [230–250 μCi (8.51–9.25- MBq, 306–336 pmol, 46–50 μg) was conducted in mice with BxPC-3 and AsPC-1 tumors to assess non-specific accumulation of the tracer.