Localization of heme oxygenase-1(HO-1) in colorectal cancer (CRC) cells. (a) is an example of well differentiated colon cancer, in which HO-1 expressed mostly in cytoplasm; arrows indicate the cytoplasmic HO-1 staining. (b) and (c) are examples of moderately differentiated colon cancer and mucinous colon cancer respectively, in which HO-1 was stained largely in cell nucleus; arrows indicate the nuclear HO-1 expression. The numbers of CRC with nuclear or cytoplasmic HO-1 expression are summarized according to different histological differentiation of CRC (d). Data are means ± SD; ***P < 0.001 (Fisher's exact test). See text for details.