Intra-abdominal fibromatosis

These lesions are probably true neoplasms;  there is molecular evidence for monoclonality^1,2

Immunohistochemistry

The fibromatoses do not have a distinct immunophenotype, but are strongly positive for vimentin and b-catenin: some show positivity for desmin and muscle actins³.

Differential diagnosis

See the immunohistochemistry of the differential diagnosis of spindle cell stromal tumours. Most lesion on the differential lack nuclear stainingfor beta-catenin:

• Low grade fibromyxoid sarcoma

• Leiomyosarcoma

• Fibrosarcoma variants:

  • myofibrosarcoma

  • classic fibrosarcoma arising in DFSP

  • inflammatory myxohyaline tumour / mxyxoinflammatory fibrobalstic sarcoma

  • myofibroma/myofibromatosis

  • nodular fasciitis

  • scars

References

¹Alman BA et al.  Aggressive fibromatosis (desmoid tumour) is a monoclonal disorder. Diag Mol Pathol 1997;6:98-101.

²Adv Anat Pathol 1997;4:317.

³Diagnostic Immunohistochemistry edited by Professor D. J. Dabbs, page 72