[68] A Contemporary Reassessment of Myxofibrosarcoma (MFS)

Ana L Ruano, Steven D Billings, John R Goldblum, Jason L Hornick, Brian P Rubin. Cleveland Clinic Foundation, Cleveland, OH; Brigham and Women's Hospital, Boston, MA

Background: Myxofibrosarcoma (MFS), also known as myxoid MFH, is a relatively common soft tissue sarcoma that typically involves the extremities of older adults. Since its original description, diagnostic criteria have varied. We have noted that deep-seated undifferentiated sarcomas with variable myxoid stroma have been increasingly misclassified as myxofibrosarcoma. Different tumor characteristics have been variably associated with clinical outcome; some grading systems seem to be more powerful predictors of prognosis than others. Recent genetic studies suggest that MFS may be characterized by loss of RB1.
Design: We conducted a single institution database search for MFS cases. After excluding recurrences and reclassifying cases that did not meet diagnostic criteria, the clinicopathological characteristics of 32 primary myxofibrosarcomas were reviewed and statistical analysis performed to identify factors predisposing to local recurrence and/or metastasis. RB1 immunohistochemistry was performed in 13 cases.
Results: The cohort included 18 (56%) females and 14 (44%) males with a mean age of 67 years (range 38-95 years). The most common location was the thigh (31%, n=10) followed by the arm (19%, n=6). Fourteen tumors (44%) were superficial, 12 (37%) deep seated and 6 (19%) had both superficial and deep components. Mean follow up was 35 months (range 23 days to 9.7 years). Nine (28%) were lost to follow up. Eight (33%) developed 1 or more recurrences and six (26%) developed metastases, with the most common site being the lung. None of the variables studied reached statistical significance with univariate analysis using Cox proportional hazard models predicting local recurrence and/or metastasis (p-values of 0.70 for depth, 0.08 for a positive margin, 0.45 for FNCLCC grade, 0.19 for size and 0.72 for percentage of myxoid stroma/cellularity). RB1 immunoreactivity was lost in 1 of 13 cases; 1 case showed a heterogeneous staining pattern.
Conclusions: In this limited study, the results suggest that positive margin status (p = 0.08) may be the most powerful predictor of recurrence and/or metastasis in myxofibrosarcoma. RB1 is lost in only a small percentage of cases. Thus, the molecular pathogenesis of most cases of MFS remains to be determined.
Category: Bone & Soft Tissue

Monday, March 4, 2013 1:00 PM

Poster Session II # 26, Monday Afternoon

 

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