CD44 in colon cancer.

Alternative splicing of ten different variant exons (v1-v10) is responsible for the creation of a large number of different CD44 surface proteins. Some of these proteins play decisive roles in the metastatic spread of rat tumours. Also in human cancers, CD44 splice variants are frequently expressed in advanced states of tumorigenesis. In breast cancer and in non-Hodgkin's lymphomas expression of exon v6 is correlated with poor prognosis of patient survival. In colorectal carcinogenesis, expression of exon v5 is an early tumour marker since it is already detectable on small dysplastic polyps (but not on normal colon epithelium). In contrast, exon v6 expression occurred with increased frequency with tumour progression, and its expression on colorectal tumours indicated reduced survival probability. Most likely, tumours carrying the CD44 v6 epitope acquire selective advantage during tumour progression and metastasis formation. This could be a proliferative advantage since mice transgenic for the CD44 isoform CD44v4-v7 on T lymphocytes show an accelerated T-dependent immune response as compared with non-transgenic siblings.