The American journal of pathology
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Sporadic aggressive fibromatosis (also called desmoid tumor) is a monoclonal proliferation of spindle (fibrocyte-like) cells that is locally invasive but does not metastasize. A similarity to abdominal fibromatoses (desmoids) in familial adenomatous polyposis and a cytogenetic study showing partial deletion of 5q in a subset of aggressive fibromatoses suggests that the adenomatous polyposis coli (APC) gene plays a role in its pathogenesis. APC helps regulate the cellular level of beta-catenin, which is a downstream mediator in Wnt (Wingless) signaling. beta-Catenin has a nuclear function (binds transcription factors) and a cell membrane function (is a component of epithelial cell adherens junctions). ⋯ Increased beta-catenin may cause the growth advantage of cells in this tumor through a nuclear mechanism. The increased protein level, relative to the RNA level, suggests that beta-catenin is degraded at a lower rate compared with normal tissues. In some cases, this is caused by a somatic mutation resulting in a truncated APC protein.