ERBB2 and neoplasm: We do not know: (i) the precise locations of their epitopes on HER2, (ii) whether any of the VHHs inhibit HER2 signaling or inhibit receptor dimerization, permitting their development as naked Ab therapeutics, (iii) whether any of the VHHs internalize into HER2+ tumor cells, permitting their development as ADCs or radioimmunotherapeutics, or (iv) whether their sequences can be humanized without loss of stability or binding affinity.