Deep
fibromatoses (
desmoid tumors) are clonal myofibroblastic proliferations that are prone to aggressive local recurrences but that do not metastasize. They must be distinguished from a host of fibroblastic and myofibroblastic lesions as well as from smooth muscle
neoplasms. Virtually all deep
fibromatoses have somatic
beta-catenin or
adenomatous polyposis coli (APC) gene mutations leading to intranuclear accumulation of
beta-catenin. Since low-grade
sarcomas in general lack
beta-catenin and since reactive proliferations would not be expected to have it, we predicted that nuclear
beta-catenin expression would be detected in deep
fibromatoses but absent in other entities in the differential diagnosis. We evaluated the role of
beta-catenin to help differentiate distinguish deep
fibromatoses from congeners.
Formalin-fixed,
paraffin-embedded sections from 21 lesions from 20 patients with deep
fibromatoses were stained with monoclonal
beta-catenin antibody (Transduction Laboratories) and compared with low-grade fibromyxoid
sarcoma (n=12),
leiomyosarcoma (n=10), various other
fibrosarcoma variants (n=13, including 3 myofibrosarcomas, 3 sclerosing epithelioid
fibrosarcomas, 5 low-grade
fibrosarcomas, 1 classic
fibrosarcoma arising in
dermatofibrosarcoma protuberans, 1 inflammatory myxohyaline
tumor/myxoinflammatory fibroblastic
sarcoma),
myofibroma/
myofibromatosis (n=12), nodular
fasciitis (n=11), and
scars (n=9). Nuclear and cytoplasmic staining was assessed. All 21 examples of deep
fibromatosis displayed nuclear
beta-catenin (focal nuclear staining in one case to 90% staining). All other lesions tested (n=67) lacked nuclear labeling for
beta-catenin, showing only cytoplasmic accumulation.
beta-Catenin immunohistochemistry separates deep
fibromatosis from entities in the differential diagnosis, a finding that can be exploited for diagnosis. Most
fibromatoses have diffuse nuclear staining although occasional examples only focally label.