AGGRESSIVE FIBROMATOSIS (DESMOID TUMOR) IS A MONOCLONAL DISORDER

Aggressive fibromatosis (also called deep fibromatosis or desmoid tumo r) is a proliferation of cytologically benign-appearing fibrocytes, of ten resulting in significant functional loss. The nature of the lesion is controversial: some evidence suggests that it is a reactive proces s, whereas other evidence supports a neoplastic etiology. The pattern of X chromosome inactivation, using a technique based on polymerase ch ain reaction (PCR) amplification of a hypervariable CAG repeat region flanking Hhal restriction sites of the human androgen receptor gene, w as determined in four cases in which cryopreserved tumor and adjacent normal tissue were available. All four tumors demonstrated a monoclona l pattern, while the adjacent normal tissues demonstrated a polyclonal pattern. This demonstrates that aggressive fibromatosis is proliferat ion of cells derived from a single clone with a growth advantage, and thus is likely a neoplastic process.