Acral myxoinflammatory fibroblastic sarcoma: case series and immunohistochemical analysis

Acral myxoinflammatory fibroblastic sarcoma (AMFS) is a rare, low-grade neoplasm most often occurring on the extremities of adults. It consists of mixed inflammatory infiltrates with nodules of epithelioid, spindled and bizarre-appearing cells within a fibrosclerotic-to-myxoid stroma. AMFS frequently recurs, but only rarely metastasizes.

A retrospective analysis of all cases of AMFS seen in the past 4 years from the Stanford University Laboratory of Surgical Pathology and collaborating institutions was performed. We sought to better characterize the clinicopathologic characteristics of this rare tumor. Immunohistochemical stains, including CD34, epithelial membrane antigen (EMA), epidermal growth factor receptor (EGFR), CD117, CD163, Ki67 and p53, were also performed.

Eighteen cases were analyzed, and clinical information was available on 13 of them. The mean age at diagnosis was 48 years old, 10/13 (77%) occurred on the distal extremities and diameter of the lesions ranged from 1.0 to 10.0 cm. Treatment included wide local or radical excision and local recurrences were not reported. Many of the lesions were multinodular. Histologic characteristics included the presence of fibrosclerotic and myxoid stroma, sheets of spindled to round epithelioid cells, Reed-Sternberg or virocyte-like cells, lipoblast-like cells and rare mitotic figures. In most cases, CD34, EGFR and CD163 were diffusely positive. EMA and CD117 were weakly positive in some cases. Ki67 labeled < 10% of cells, and staining with P53 was variable.

Because AMFS may be mistaken for lymphoma, infection or tumors with higher metastatic potential, correct diagnosis is important to avoid unnecessary procedures and allow for proper clinical management. EGFR positivity suggests possible therapeutic use in aggressive cases.