Immunohistochemical expression of ABC proteins in positive controls and call tumors. A. Canalicular staining pattern of MDR1 in liver (positive control). B. MDR1 is not expressed in the HRS cells of CHL (white arrows); endothelial cells are positive (black arrow). C. Canalicular staining pattern of ABCC2 in liver (positive control). D. HRS cells are negative for ABCC2; endothelial cells and scattered lymphocytes are positive. E. Hepatocytes show cytoplasmic expression of ABCC3 (positive control). F. HRS cells are negative for ABCC3.