Intra-abdominal fibromatosis

These lesions are probably true neoplasms;  there is molecular evidence for monoclonality1,2

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 staining for b-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