CD44s, CD44v6, and CD44v9 expression in primary GC by IHC staining. Representative images from three cases for the expression of each CD44 isoform are shown. (A and D), (B and E), and (C and F) are from the same patient. (A) Positive staining for CD44s both in whole tumour sections and at the ITF in GC with serosal exposure. (original magnification: × 40); (B) Positive staining for CD44v6 at the mucosal layer, but negative staining at the ITF of submucosal invasive GC. (C) Negative staining for CD44v9 in the surface layer, but positive staining at the ITF of muscularis propria invasive GC. (original magnification: × 40). In the high-power field, the expression of each CD44 isoform was identified along the membrane of cancer cells (D–F). (original magnification: × 200). Abbreviations: CD44s=CD44 standard isoform; CD44v6=CD44 variant isoform 6; CD44v9=CD44 variant isoform 9; GC=gastric cancer; IHC=immunohistochemistry; ITF=invasive tumour front.