1C1m-Fc, a promising anti-TEM-1 DOTA conjugate, was labeled with ⁶⁴ Cu to target cancer cells for PET imaging and predicting the efficacy and safety of a previously studied [ ¹⁷⁷ Lu]Lu-1C1m-Fc companion therapy. DOTA-conjugated 1C1m-Fc was characterized by mass spectrometry, thin layer chromatography and immunoreactivity assessment. PET/CT and biodistribution studies were performed in human neuroblastoma xenografted mice. Absorbed doses were assessed from biodistribution results and extrapolated to ¹⁷⁷ Lu based on the [ ⁶⁴ Cu]Cu-1C1m-Fc data. The immunoreactivity was ≥ 70% after 48 h of incubation in serum, and the specificity of [ ⁶⁴ Cu]Cu-1C1m-Fc for the target was validated. High-resolution PET/CT images were obtained, with the best tumor-to-organ ratios reached at 24 or 48 h and correlated with results of the biodistribution study. Healthy organs receiving the highest doses were the liver, the kidneys and the uterus. [ ⁶⁴ Cu]Cu-1C1m-Fc could be of interest to give an indication of ¹⁷⁷ Lu dosimetry for parenchymal organs. In the uterus and the tumor, characterized by specific TEM-1 expression, the ¹⁷⁷ Lu-extrapolated absorbed doses are overestimated because of the lack of later measurement time points. Nevertheless, 1C1m-Fc radiolabeled with ⁶⁴ Cu for imaging would appear as an interesting radionuclide companion for therapeutic application with [ ¹⁷⁷ Lu]Lu-1C1m-Fc.