In BxPC-3 xenografts (Fig. 4B and Supplementary Table S3), exposure to cetuximab showed no difference in 89Zr-MEHD7945A uptake between control (28.56 ± 10.81%ID/g) and cetuximab-blocked tumors (21.79 ± 14.19%ID/g, p = 0.39). Competition of the tracer with DL3.6b demonstrated an approximately two-fold increase in radiotracer accumulation of 46.89 ± 20.1%ID/g (p = 0.0021).