ATP7A and melanoma: They determined the MC1 and αvβ3 integrin receptor densities on M21 human melanoma cells and revealed that 1281 MC1 receptors/cell and 96,555 αvβ3 integrin receptor/cell presented on M21 human melanoma cells [114], making the M21 human melanoma xenografts a suitable animal model to examine the dual-receptor-targeting capacity of a 99mTc-labeled RGD-conjugated α-MSH hybrid peptide.