Extra-Abdominal Fibromatosis (Desmoid Tumor)
Some cases of fibromatosis show myxoid matrix. Majority of the deep-seated fibromatoses show mutations in beta-catenin or APC genes - both of which are components of WNT signaling pathway. This results in nuclear accumulation of beta-catenin. The myofibroblastic cells are also positive for vimentin, SMA, MSA, calponin, desmin (rare cases, focally) and negative for CD34.