Frequent loss of SMAD4/DPC4 protein in colorectal cancers.

Loss of DNA sequences from chromosome 18q21 is a major genetic change in colorectal tumorigenesis. Multiple genes have been identified in this area. One of these, DPC4 (deleted in pancreatic cancer 4, also known as SMAD4), is mutated in a minor subset of colorectal carcinomas as well as in germlines of humans predisposed to colon tumours. The involvement of SMAD4 in sporadic colorectal neoplasia was evaluated by immunohistochemistry in 53 unselected cases and 27 cases displaying microsatellite instability. SMAD4 expression was absent in 20 of 53 (38%) unselected colorectal carcinomas, and reduced in another 15 (28%) cases. However, 26 of 27 cancers displaying microsatellite instability and TGF-betaIIR mutations were positive for SMAD4 immunostaining. Loss of SMAD4 expression may play a more prominent role in colon cancer than anticipated based on genetic evidence, but not in mutator phenotype tumours.