Immunohistochemical labeling for Dpc4 mirrors genetic status in pancreaticadenocarcinomas - A new marker of DPC4 inactivation

DPC4 (MADH4, SMAD4) is a tumor suppressor gene inactivated by allelic loss in approximately 55% of pancreatic adenocarcinomas, Unfortunately, it can b e technically very difficult to detect the inactivation of DPC4 at the gene tic level because genetic analyses require the microdissection of relativel y pure samples of neoplastic and normal tissues, This is especially true fo r pancreatic adenocarcinomas, which elicit vigorous, non-neoplastic, stroma l responses. Immunohistochemical labeling can overcome this hurdle because it preserves morphological information, We therefore studied the expression of the DPC4 gene product in 46 cancers, including 5 cancer cell lines by W estern blot analysis and 41 primary periampullary adenocarcinomas by immuno histochemistry. The status of exons 1-11 of the DPC4 gene in all 46 of the cancers had been previously characterized at the molecular level, allowing us to correlate Dpc4 expression directly with gene status, Three cell lines had wild-type DPC4 genes, and Dpc4 expression was detected in all three by Western blot, The two cell lines with homozygously deleted DPC4 genes did not show Dpc4 protein by Western blot analysis. Immunohistochemical labelin g revealed that 17 (94%) of the 18 primary adenocarcinomas with wild-type D PC4 genes expressed the DPC4 gene product, whereas 21 (91%) of 23 primary a denocarcinomas with inactivated DPC4 genes did not. Cases in which there wa s discordance between the immunohistochemical labeling and the genetic anal yses were reanalyzed genetically, and we identified a deletion in exon 0 of DPC4 in one of these cases, This is the first report of a mutation in exon 0 of DPC4 in a pancreatic cancer. The contrast between the strong expressi on of Dpc4 by normal tissues and the loss of expression in the carcinomas w as highlighted in several cases in which an infiltrating cancer was identif ied growing into a benign duct, These observations suggest that immunohisto chemical labeling for the DPC4 gene product is an extremely sensitive and s pecific marker for DPC4 gene alterations in pancreatic carcinomas. The sens itivity and specificity of immunohistochemical labeling for Dpc4 in other p eriampullary carcinomas has yet to be determined.