PGP and melanoma: In further studies of M14 cell line variants (specifically, MDR1/P-gp-positive drug-resistant M14 ADR compared with MDR1/P-gp-negative drug sensitive M14 cells), members of the same research group have more recently reported MDR1/P-gp to be linked with MAPK signalling and to be involved in melanoma cell migration and invasion (Colone et al, 2008).