DCC and SMAD4 Alterations in Human Colorectal and Pancreatic Tumor Dissemination

Chromosome 18q is lost a high proportion of colorectal and pancreatic cancers. Three candidate tumor suppressor genes, DCC, Smad4 and Smad2 have been identified in this chromosome region. DCC and Smad4 aberrations have been previously identified in pancreatic and colorectal tumors. The aim of this study was to compare the presence of concurrent genetic aberrations in DCC and neighboring Smad4 and Smad2 genes during colorectal and pancreatic distal dissemination. We have used a panel of orthotopically implanted colorectal and pancreatic xenografts and corresponding metastases. We have shown that while LOH at DCC locus occurred at a similar frequency in both tumors, diminished DCC protein expression was exclusively present in colorectal tumors harboring intragenic DCC LOH. In contrast, in pancreatic xenografts loss of DCC protein and mRNA expression was restricted to metastases. Smad4 gene aberrations were detected at a similar frequency in both tumors and were selected for during distal dissemination. Acquisition of alterations in both genes occurred independently. Our results suggest that both DCC and Smad4 contribute to pancreatic and colorectal distal dissemination. However, the role of DCC may differ between both tumor types.