Overexpression was also confirmed on RNA levels of both transporters, especially the ABCB4, implicating that chronic cholestatic disease may lead to upregulation of ABCB11, and more evident ABCB4, potentially as a compensatory mechanism to remove the overload of toxic bile constituents, which accumulated during period of long-lasting chronic cholestasis in PSC. The gene discussed is ABCB4; the disease is pancreatic serous cystadenoma.