Identification and progression of a desmoid precursor lesion in patients with familial adenomatous polyposis.

BACKGROUND: Desmoid tumours occur in about 10 per cent of patients with familial adenomatous polyposis (FAP), and are an important cause of morbidity and death. The natural history of desmoids was investigated by documenting prospectively the prevalence and progression of possible precursor lesions.
METHODS: A group of patients with FAP and controls were examined at laparotomy. Another group, with FAP and no clinical evidence of desmoid, and a group of controls, underwent abdominopelvic computed tomography.
RESULTS: At laparotomy 13 of 42 patients with FAP had fibromatous mesenteric plaques; seven of these had not had surgery. Seven had more extensive mesenteric fibromatosis and had undergone significantly more laparotomies than the rest. Of 103 patients scanned, two had desmoid tumours and 22 (21 per cent) had mesenteric fibromatosis. On follow-up both desmoid tumours grew rapidly; mesenteric fibromatosis was unchanged in eight and resolved in four of the 12 patients rescanned.
CONCLUSION: A model of desmoid tumour development is suggested, analogous to the adenoma-carcinoma sequence, in which a less benign phenotype emerges as molecular genetic abnormalities accumulate: mesenteric plaque-like desmoid precursor lesions arise in many patients with FAP before surgery as a result of abnormal fibroblast function; some, perhaps stimulated by surgery, progress to mesenteric fibromatosis; these in turn can give rise to desmoid tumours.