PGP and neoplasm: Assessing the expression of these efflux pumps in the cohort of primary tumours alone (Table 5) showed similar trends to those seen when evaluating all 134 cases, that is, MDR1/P-gp expression being associated with spread to the lymph nodes (P=0.049) and increasing Breslow's depth (although NS, P=0.056), with MRP-1 expression being significantly associated with increasing Clark's level (P=0.023).