Low-grade fibromyxoid sarcoma: a report of eight cases with histologic, immunohistochemical, and ultrastructural study.

We present eight cases of low-grade fibromyxoid sarcoma (LGFS) of soft tissues. The patients, six men and two women, ranged in age from 28 to 44 years (median, 39 years). All tumors were subcutaneous. They were located in the lower extremity (three cases), inguinal/perineal region (two cases), trunk (one case), upper extremity (one case), and neck (one case). Grossly, the lesions were similar to those described in previous studies; fibrous and well circumscribed, with pseudocapsules, and without any necrosis or nodularity. In a single case of hemosiderin-rich tumor, rusty brown strips were seen on the cut surface. Histologically, the tumors were composed of alternating fibrous and myxoid areas with various cellularity and with swirling and whorled growth patterns. The cells were stellate or spindle shaped and displayed none to mild nuclear pleomorphism and hyperchromasia. Some hypercellular areas showed a fascicular or herring bone pattern similar to common fibrosarcomas. In addition to the known typical picture of LGFS, we also have seen some unusual features. The cells of myxoid areas were often arranged in rows, thus resembling ossifying fibromyxoid tumor or myxoid chondrosarcoma of soft tissues. In a single case, the tumor cells contained a large amount of hemosiderin and the cellular nests contained synovial metaplasia-like clefts. The intranuclear invaginations of cytoplasm represented another interesting finding that was present in all tumors in our series. They seem to be constant or at least frequent features of LGFS, which may assist in the differential diagnosis. The immunohistochemical and ultrastructural findings were consistent with the fibroblastic nature of LGFS. Four cases also showed features of possible histiocytic modulation of the neoplastic fibroblasts.