Desmoid-type fibromatosis in a boy with Down syndrome.

Patients with Down syndrome (DS) have a markedly higher incidence of childhood leukemia, but a lower incidence of most solid tumors, compared with age-matched euploid individuals. Trisomy 21 might be protective against tumorigenesis because of several tumor suppressive mechanisms. Desmoid-type fibromatosis (DF) is a rare monoclonal, fibroblastic proliferation characterized by a variable clinical course. In recent reports, almost all cases of DF involved genomic alterations associated with activation of the Wnt/β-catenin pathway. Here, we report the case of a boy with DS who developed DF without activation of the Wnt/β-catenin pathway. To the best of our knowledge, this is the first case of DS involving DF.