Comparison of immunohistochemistry and RT‐PCR for detection of CD44v‐expression, a new prognostic factor in human breast cancer

In different human tumors, splice variants of the surface glycoprotein CD44 (CD44v) are correlated with advanced stages of tumor growth and metastatic potential. In breast cancer and colon cancer, expression of epitopes encoded by exon v6 on primary tumors is an independent prognostic factor for poor patient survival. Two different screening methods for the detection of CD44 variants in tumors have been applied: immunohistochemistry (IHC) and semi‐quantitative reverse transcription PCR (RT‐PCR). In this study, we have compared the predictive capacity and the applicability of both approaches, using 31 human breast‐tissue specimens (normal and neoplastic). IHC reveals lack of expression of CD44v on normal ductal epithelial cells but strong expression on myoepithelial cells. The majority of tumors express CD44 epitopes encoded by several variant exons. RT‐PCR detects splice variants in normal epithelium, probably derived from RNA expressed in the myoepithelium. In tumors, RT‐PCR reveals expression of a wide range of splice variants, including new ones that are not detected in normal breast tissue, e.g. ones that contain all variant exons. The conclusion of this comparison is that IHC is the better method for breast‐tumor sample screening but that the increased sensitivity of RT‐PCR can help to distinguish CD44v‐positive from CD44v‐negative tumors in cases where only a few tumor cells express variants or where epitopes are masked.