ABCB1 and neoplasm: The expression of p-glycoprotein, CD44s (CD44 standard), and its CD44v6 isoform (CD44 variant 6), which are associated with tumor biology and the development of metastases, and the expression of the CD95/Fas, Fas-L (Fas ligand) and p53 that are directly involved in cell apoptosis (Figure 1E), were also studied in tumor samples.