H&E section of the colonic carcinoma showing that the tumor is poorly differentiated with a solid growth pattern (A). By immunohistochemistry, the tumor cells are positive for cytokeratin CAM5.2 (B); they show loss of staining for MLH1 (C), PMS2 (D), MSH2 (E), and MSH6 (F) with appropriate positive internal control for each of the 4 stains (all figures at 200× magnification; scale bar, 500 μm).