CD44 and breast cancer: To further validate a role for CD44 in the development of an aggressive breast cancer cell phenotype and to begin to explore any differential contribution of CD44 isoforms, we overexpressed CD44v3 and CD44v6, two specific isoforms we have shown to be upregulated in Tam-R and Fas-R cells, separately in MCF-7 cells and assessed any changes to cellular phenotype.