ERBB2 and breast cancer: When used as secondary detection reagent on BT-474 breast cancer cells, which strongly overexpress HER2, the labelled GFP-clamps resulted in a specific signal, very similar to that of a commercially available rat monoclonal antibody (FM264G) (Fig. 6(a)), which, however, may crosslink GFP and thus also the bound receptor and may thus elicit unintended biological consequences.