Acral myxoinflammatory fibroblastic sarcoma

Acral myxoinflammatory fibroblastic sarcoma (AMSF), also termed myxoinflammatory fibroblastic sarcoma (MSF), is a rare, low-grade, soft tissue tumor that the World Health Organization (2020) classified as in the category of rarely metastasizing fibroblastic and myofibroblastic tumors.^[1] 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.^[2]

AMSF tumors commonly develop in the subcutaneous tissues of the arms or legs of adults with an equal incidence (~1 per million individuals^[2]) in males and females.^[3] These tumors are composed of a prominent inflammatory cell infiltrate admixed with cells that have highly variable microscopic appearances,^[4] including, in particular, distinctively large, neoplastic epithelioid cells, i.e. cells resembling epithelial cells,^[5] and lipoblast-like fibroblastic cells containing multiple vacuoles.^[6] The variable microscopic appearances of AMSF tumors have made them difficult to correctly diagnose in many cases.^[4]

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.^[2]