Tumor specimens from 14 patients surgically treated for aggressive fibromatosis (6 familial adenomatous polyposis and 8 sporadic cases), analyzed for adenomatous polyposis coli (APC) and CTNNB1 (beta-catenin) mutations, were further investigated for beta-catenin, cyclooxygenase-2 (COX-2), platelet-derived growth factor (PDGF) receptor alpha (PDGFRA)/PDGF receptor beta (PDGFRB), their cognate ligands (PDGFA and PDGFB), and KIT using a comprehensive immunohistochemical, biochemical, molecular, and cytogenetic approach.