Thus far, radiocobalt-labeled DOTA-ZEGFR:2377 for PET imaging provided the best contrast among all studied anti-HER1 affibody variants in mice with A431 xenografts, with an impressive tumor-to-liver ratio of 3.1 ± 0.5 at 3 h pi [105,120,139,140,141,142,145,146,147]. Here, EGFR is linked to neoplasm.