Description: The purpose of this study was to investigate the expression of carcinoembryonic antigenrelated cell adhesion molecule 5 (CEACAM5) and correlate it with OPN expression andfunction in squamous carcinoma of tongue.Paraffin were sections of 80 samples with squamous carcinoma of tongue and 40 sampleswith normal tissue of tongue for benign lesion having undergone surgery.Immunohistochemistry (IHC) was used to study the distribution of CEACAM5 and OPN, anddouble-labeling immunohistochemistry was used to observe the relationship betweenCEACAM5 and OPN expression.CEACAM5 and OPN are found in normal tissue of tongue, but with different expressionpattern. CEACAM5 expression mainly with membranous staining is restricted on thesuperficial epithelium. However, OPN expression with mainly cytoplasmic staining isrestricted on the deep epithelium. No colocalization of CEACAM5 and OPN have beenobserved in normal tissue of tongue. In squamous carcinoma of tongue, CEACAM5expression with cytoplasmic staining is different from normal tongue tissue withmembranous staining, and the transformation of CEACAM5 distribution from membrane tocytoplasm is an important incident for the invasion and differentiation of tumor. CEACAM5and OPN are colocalized in cytoplasm, and a significant correlation was observed betweenthe positive colocalization and the negative colocalization in the depth of invasion and thedifferentiation of the tumor.