Low-grade fibromyxoid sarcoma: a clinicopathologic study of 18 cases, including histopathologic relationship with sclerosing epithelioid fibrosarcoma in a subset of cases.

Low-grade fibromyxoid sarcoma (LGFMS) is an uncommon tumor with diverse histopathologic features. It has been found to be histopathologically and genetically related to hyalinizing spindle cell tumor with giant rosettes. Lately, sclerosing epithelioid fibrosarcoma (SEF) has been identified as another rare variant of fibrosarcoma. Very few studies have addressed the aspect of its histopathologic relationship with LGFMS. The present study was conducted to critically analyze the clinicopathologic features of a series of LGFMS cases, including identification of cases with histopathologic similarity with SEF. During a 7-year period, 18 LGFMS cases were diagnosed in 9 male and 9 female patients, had ages ranging from 10 to 69 years (median, 32.5 years), and were most commonly identified in the lower extremities (8 cases, or 44.4%). Most cases (16, 88.8%) showed "classic" features of LGFMS with mild (13 cases, or 72.2%) to moderate atypia (5 cases) and nil mitosis (12 cases, or 66.6 %). Variable features included whorling tumor growth pattern, small rosettes, perivascular hyalinization, and amianthoid-like collagen, along with epithelioid differentiation and nuclear pseudoinclusions within tumor cells. Four cases (22.2%) with large collagenous rosettes were diagnosed as hyalinizing spindle cell tumor with giant rosettes. Distinct SEF-like areas were observed in 6 cases (33.3%). On immunohistochemistry, consistent vimentin positively reinforced fibroblastic lineage of the tumor. Therapeutically, all 4 of 7 cases with available follow-up details, which underwent wide excisions, have been free of disease at 5 to 61 months. Eight excisions with unclear margins included 3 cases free of disease (24, 36, and 52 months) and 1 case with recurrence and metastasis. Two cases of marginal excision had tumor recurrences, including 1 case that recurred after 10 years. Low-grade fibromyxoid sarcoma is an uncommon sarcoma with diverse histopathologic features. Histopathologic relationship exists between LGFMS and SEF in a few cases. An LGFMS is optimally managed with surgical wide excision and follow-up.