ABCC1 and melanoma: MRP-1 expression was also significantly associated with spread to the lymph nodes (P<0.0005) and with more extensive invasion of the melanoma, i.e., when comparing MRP-1 expression in specimens with Clark's level II, III and IV vs Clark's level V; P=0.032 (incidentally, comparison of MRP-1 expression in those specimens with Clark's levels II and III with that in specimens with Clark's levels IV and V also supported the association between MRP-1 expression and increasing stages of disease; (although NS, P=0.051)).