OBJECTIVETo study the clinicopathologic features, immunophenotypes and differential diagnosis of myxoinflammatory fibroblastic sarcoma (MIFS).

METHODSThe clinical and pathologic features of 6 cases of MIFS were analyzed. Immunohistochemical study was performed using the standard EnVision method.

RESULTSThere were altogether 2 adult males and 4 adult females (median age = 47 years and mean age = 50 years). Three cases were located in the lower extremities, 2 in the upper limbs and 1 in the axillary region. Common presentation included slowly growing mass or swelling in the extremities, accompanied by mild pain or tenderness. Grossly, the tumor appeared multinodular and ranged from 2.5 cm to 4.6 cm in diameter (mean = 3.4 cm). Microscopically, there was a dense inflammatory infiltrate merging with hyaline and myxoid zones in various proportions. Spindle-shaped tumor cells were seen admixed with large atypical cells which distributed singly or in small clusters, amongst an inflammatory, hyaline or a myxoid background. These atypical cells had large nuclei and prominent nucleoli, resembling virocytes, Reed-Sternberg cells or ganglion cells. Mitotic figures were rarely identified. Extracellular mucin associated with scattered monovacuolated or multivacuolated lipoblast-like cells was noted. Immunohistochemically, these bizarre cells were consistently positive for vimentin, but negative for a panel of antibodies including LCA, CD15, CD30, CD34, CD68, S-100, HMB45, AE1/AE3, smooth muscle actin and desmin. Follow-up result was available in 4 cases; and 2 of them showed local recurrence after an incomplete excision. There was no evidence of distant metastasis.

CONCLUSIONSMISF is a low-grade sarcoma of fibroblastic differentiation. Awareness of the clinical and pathologic characteristics is helpful in arriving at the correct diagnosis and distinction from benign inflammatory fibromyxoid lesions.