CD44v3 and CD44v6 expression activity in human xenograft CRC metastatic and liver colonisation system. A. CD44v3 and v6 gene expression activity of primary and metastatic human colon carcinoma xenograft tumours (HT29, HT25 and HCT116) implanted orthotopically (colonic wall)into scid mice. The three genetically different human colorectal carcinoma lines showed three different behaviours in terms of CD44v3 and v6 expression rate changes during metastatic process. The reason of it might be the baseline level of expression in prmary tumours: relative expression rates (CD44v3 and v6 expression normalized on β-actin expression rates) of the three tumour types showed 1–1 order of magnitude differences. As we measure summated expression rates (average) of each tumour cells of the particular tumour mass, differences in CD44 variant exon expression levels might be explined with differences of CD44v3/v6 high cell proportion of the tumour cell mass. B. Model of metastatic clone selection in each three cell lines, schematic explanation of the differences in a consequent model.