Intrathoracic sporadic desmoid tumor with the beta-catenin gene mutation in exon 3 and activated cyclin D1.

We report a case of intrathoracic desmoid tumor without familial adenomatous polyposis and demonstrate beta-catenin mutation of exon 3. A 15-year-old male presented with a desmoid tumor after having sustained an assault. In an examination for a mutation of the beta-catenin gene, an activating mutation from ACC (Thr) to GCC (Ala) at codon 41 was found. Immunohistochemical staining showed that accumulated beta-catenin protein was predominantly localized in the nuclei of desmoid cells, and cyclin D1 protein was also overexpressed. These findings might suggest that an activating mutation of the beta-catenin gene affected regulation of the cyclin D1 gene, resulting in the generation of intrathoracic sporadic desmoid tumor, which arose at the site of posttraumatic injury.