anti-Caudal Type Homeobox 2 (CDX2) (N-Term) antibody: CDX2 is a transcription factor which regulates proliferation and differentiation of intestinal mucosa. In adults the expression of CDX2 is usually limited to intestinal epithelium. Immunohistochemically, the protein is detectable in nuclei of normal intestinal epithelium. Loss of CDX2 correlates with loss of differentiation in colorectal tumours. Anti-CDX2 antibody is very useful in identifying the origin of metastatic adenocarcinomas and carcinoids. Some mucinous carcinomas of the ovary also stain positive with this CDX2 antibody as well as some carcinomas from the upper gastroinstestinal tract (see Moskaluk et al. 2003). Immunohistochemistry (IHC) is a complex technique in which immunological and histological detection methods are combined. In general, the manipulation and processing of tissues before immunostaining, especially different types of tissue fixation and embedding, as well as the nature of the tissues themselves may cause inconsistent results (Nadji and Morales, 1983). Endogenous pseudoperoxidase and peroxidase activity or endogenous biotin and alkaline phosphatase activity can cause non-specific staining results depending on the detection system used. Tissues that contain Hepatitis B surface antigen (HBsAg) can produce false positives when using HRP detection systems (Omata et al, 1980). Insufficient contrast staining and/or improper mounting of the sample may influence the interpretation of results.