Analysis of E-cadherin in diffuse-type gastric cancer using a mutation-specific monoclonal antibody

In-frame deletions from the E-cadherin mRNA, coding for a hemophilic cell a dhesion molecule, are characteristic for diffuse-type gastric carcinomas. U sing immunohistochemical analysis the mutant form cannot be distinguished f rom normal E-cadherin, making results difficult to interpret. In this study , a rat monoclonal antibody, designated E-cad delta 9-1, was generated agai nst a peptide spanning the fusion junction region between exons 8 and 10. T his new epitope is present in an E-cadherin variant that lacks exon 9 from the mRNA due to different splice-site gene mutations. Using Western blottin g and immunohistochemistry of E-cadherin-transfected cells, we demonstrate that E-cad delta 9-1 specifically reacts with E-cadherin lacking exon 9 but not with the wildtype protein. No immunoreactivity was observed in 31 nont umorous and embryonal tissues analyzed. In gastric carcinoma specimens know n to express mutant E-cadherin mRNA lacking exon 9, E-cad delta 9-1 targets exclusively tumor cells in routine formalin-fixed and paraffin-embedded ma terial from biopsies, primary tumors, and lymph node metastases. In a retro spective series of 172 diffuse-type gastric carcinomas expressing E-cadheri n, E-cad delta 9-1 reacted with 22 tumors (13%). This new tumor marker-mono clonal antibody system could open novel avenues for selective diagnosis and specific therapy of a subgroup of diffuse-type gastric cancer patients.