Acral myxoinflammatory fibroblastic sarcoma
Acral myxoinflammatory fibroblastic sarcoma, also termed myxoinflammatory fibroblastic sarcoma, is a rare, low-grade, soft tissue tumor that the World Health Organization classified as in the category of rarely metastasizing fibroblastic and myofibroblastic tumors. It is a locally aggressive neoplasm that often recurs at the site of its surgical removal. However, it usually grows slowly and in only 1–2% of cases spreads to distant tissues.
AMSF tumors commonly develop in the subcutaneous tissues of the arms or legs of adults with an equal incidence in males and females. These tumors are composed of a prominent inflammatory cell infiltrate admixed with cells that have highly variable microscopic appearances, including, in particular, distinctively large, neoplastic epithelioid cells, i.e. cells resembling epithelial cells, and lipoblast-like fibroblastic cells containing multiple vacuoles. The variable microscopic appearances of AMSF tumors have made them difficult to correctly diagnose in many cases.
AMSF lesions are treated by surgical resection with the goal to remove all tumor tissue in order to reduce local recurrences. Repeated local recurrences are treated by repeated surgical resections. In extreme cases, a combination of radiation therapy with surgical resection or amputation of an involved appendage has been used to treat these tumors. Chemotherapy of localized, recurrent, and/or metastatic disease has not yet been shown to be a useful treatment strategy for AMSF.
Presentation
AMSF tumors typically occur in adults, but have been reported in individuals aged 4 to 91 years. Individuals commonly present with a subcutaneous or less commonly intramuscular tumor located in an acral, dorsal of a limb: about two-thirds of cases occur in a finger, hand, wrist, foot, or ankle. In a minority of cases, these tumors have developed in the upper arm, thigh, shoulder, inguinal area, upper back, neck, temple area of the head, and in one case, the nose. Individuals commonly present with a painless, slowly growing mass in one of these areas. The size of these tumors has ranged from 1.5 to 18 cm, although one AMSF tumor that spanned the supraclavicular and infraclavicular fossa areas had a maximum diameter of 25 cm and another AMSF tumor in the thigh had a maximum diameter of 30 cm. Individuals often re-present with a recurrence of their tumor at the site of its previous surgical removal or, in rare cases, present with metastatic disease.Pathology
As examined by gross pathology, AMSF tumors are typically lobulated, with gelatinous, fleshy, or firm areas that vary in color and texture; they are most often localized to subcutaneous adipose tissue but may infiltrate into nearby tissues. Histopathologic microscopic examinations of hematoxylin and eosin stained tumors characteristically show spindle-shaped cells admixed with prominent inflammation-like areas containing a mixture of neutrophils, lymphocytes, and plasma cells. The areas of these lesions that contain spindle cells are often also occupied by distinctively large, variably-shaped epithelioid cells that have vesicle-laden nuclei and acidophilic nucleoli. These cells have been termed Reed-Sternberg cell-like, virocyte-like, and ganglion cell-like. The tumors may also contain large vacuolated pseudolipoblasts. These various cell types are embedded in a myxoid and collagen fiber-laden tissue background. In addition to the cited cell types, the tumors may contain degenerated, dying, and or dead cells and large histiocyte-like cells that have engulfed other cells, usually neutrophils The proportions, numbers, and types of these cells varies greatly among cases and thereby may present diagnostic challenges. For example, AMSF tumors can have dense inflammatory infiltrates which obscure other cell types and thereby suggest that the lesion is a purely inflammatory reaction.A recent immunohistochemical immunostaining small study on AMSF tumor tissue detected cells that expressed the vimentin protein in almost all cases; expressed MUC1, CD31, CD34, CD68, and PDPN proteins in a variable number of cases; and did not express CD45, CD15, CD30, HMB-45, MLANA, desmin, GFAP, or S100 proteins. Earlier studies had reported that these cells express vimentin, periodic acid-Schiff, CD34, CD68, and S100 proteins in many cases but not MUC1, cytokeratin, or desmin proteins. The expression profiles of these proteins, which sometimes differed in different studies, have not been helpful in identifying a tumor as an AMSF.