The observed associations between expression of these efflux pumps and the more aggressive phenotype of melanoma, together with the significantly higher prevalence of these pumps (MRP-1, in particular) in metastases compared with primary specimens, suggests that MRP-1 and MDR1/P-gp may contribute, at least to some extent, to the incurable nature of malignant melanoma. This evidence concerns the gene PGP and melanoma.