Our previous work demonstrated that the probe detected solely HER3 feedback upon AKT inhibition in triple negative breast cancer51. Moreover, we have unpublished data showing similar HER3 detection by the radiotracer in colorectal cancer upon MEK treatment. Our findings were corroborated by a wide body of evidence demonstrating HER3 feedback upon independent blockade of EGFR in colon cancer12, head and neck small cell cancer13, lung cancer52 and triple negative breast cancer. Thus, simultaneous blockade of both EGFR and HER3 with MEHD7945A is potentially more efficacious than single agent monotherapy.