Myxoinflammatory Fibroblastic Sarcoma

The findings are those of a very unusual histiocytoid proliferation with bizarre large multinucleated cells of which many exhibit emperipolesis in a characteristic highly inflammatory background composed of lymphocytes and plasma cells in a variable sclerotic and somewhat myxomatous matrix. Overall the combined light microscopic and phenotypic profile would be most compatible with the categorization of this lesion as a very rare form of sarcoma namely the myxoinflammatory fibroblastic sarcoma.

These lesions do have a highly characteristic cytogenetic signature characterized by rearrangement of the TGF-beta-R3 and MGEA-5 genes. There is a significant degree of overlap with two other entities namely the pleomorphic hyalinizing angiectatic tumor and the hemosiderotic fibrolipomatous tumor. Interestingly the cytogenetic pattern in this neoplasm is similar to the hemosiderotic fibrolipomatous tumor while the pleomorphic hyalinizing angiectatic tumor does appear to be cytogenetically distinct to indicate that it is an entity that is quite separate from the myxoinflammatory fibroblastic sarcoma. This entity was first described by Sharon Weiss and coworkers under the appellation of myxohyaline tumor of the distal extremities with atypical virocyte/Reed-Sternberg-like cells.

Click images to begin the slideshow

Slide 1: 33 year old woman with a distal extremity soft tissue mass. The excision specimen shows a fairly well circumscribed tumorous process involving the soft tissue.

Slide 2: The tumor is characterized by a background of marked inflammation including sheets of plasma cells, many neutrophils as well as lymphocytes with a background of neovascularization and variable fibrosis.

Slide 3: Scattered within the inflammation are many histiocytes of which many have bizarre features.

Slide 4: Zones of fibroplasia are associated with a reduction in the extent of inflammatory cell infiltration and, in fact, assume a somewhat orderly onion-skin pattern of fibrosis.

Slide 5: These histiocytes are predominantly mononuclear having voluminous cytoplasms whereby the cytoplasms have a biphasic tinctorial quality characterized by peripheral eosinophilia with more of a perinuclear glassy amphophilic alteration of the cytoplasm. These cells are very large and exhibit a striking pattern of emperipolesis whereby the ingested inflammatory cells almost obscure the cellular detail. <br><br>Amidst these large histiocytoid cells exhibiting emperipolesis are cells with bizarre nuclear features. These cells are excessively large with marked nuclear contour irregularities, hyperchromasia and macroeosinophilic nucleolation really exhibiting severe pleomorphism.

Slide 6: Bizarre cell with macroeosinophilic nucleolation.

Slide 7: Tumor cells are excessively large with marked nuclear contour irregularities, hyperchromasia and macroeosinophilic nucleolation really exhibiting severe pleomorphism. Emperipolesis is also present.

Slide 8: There is extensive immunoreactivity for CD163 (shown here) largely reflecting staining in small reactive lymphocytes however at least a subset of the larger histiocytoid forms exhibiting emperipolesis demonstrates CD163 positivity. Part of the positive reaction reflects the ingested inflammatory cells. <br><br>The cells are not CD1A positive. They do not stain for CD35. They are not CD30 positive.

Slide 9: While the cytokeratin 5/6 preparation is negative there is staining of the atypical histiocytoid cells including those exhibiting emperipolesis with cytokeratin 7 (shown here).

Slide 10: There is extensive staining for Factor XIIIA including the large histiocytic forms exhibiting emperipolesis and the many more bizarre sarcomatoid appearing histiocytes are positive for Factor XIIIA.