CTNNB1 mutations are highly prevalent and were detected in 84 to 87% of all sporadic fibromatosis/desmoid tumors. Most CTNNB1 mutations in fibromatosis/desmoid tumors are predominantly missense mutations in codons 41 and 45 of exon 3. These mutations result in β-catenin stabilization, increased nuclear accumulation and activation of the Wnt signaling pathway. Specific CTNNB1 mutations have been reported to predict recurrence in some cases of extra-abdominal and abdominal aggressive fibromatosis. A S45F mutation increased the risk of recurrence significantly.