The expression data may not be conclusive, as MDR capacity in cancer cells is determined not only by the expression of plasma membrane transporters of the ABC family, but by a multitude of other factors, including the composition and the fluidic state of plasma membrane, the presence of relevant cofactors, modulators, etc. Thus, the commonly-used assessment of MDR capacity through the analysis of transporter expression was found to be unreliable in a number of cases [6]–[8]. Here, ABCB6 is linked to cancer.