The Clinicopathologic Spectrum of Myxoid and Round Cell Liposarcoma. A Study of 95 Cases

Background: The prognosis of patients with myxoid liposarcoma (ML) or round cell liposarcoma (RCL) has never been adequately defined.

Methods: We evaluated the clinical and pathologic features of 95 patients with biopsy proven ML or RCL examined at the Mayo Clinic between 1971 and 1992. Routine hematoxylin and eosin stained slides of all cases were reviewed. Morphologic variable evaluated included percent of round cell differentiation, percent of lipoblastic differentiation, and presence of tumor necrosis. Clinical follow-up was available for 86 patients (range: 6 months-23.4 years; mean: 7.2 years; median: 5.9 years). Flow cytometry for determination of DNA ploidy was performed on paraffin embedded tissue available from 46 cases. Survival analyses for the 86 patients with adequate clinical follow-up were performed by the Kaplan-Meier test using the approximate chi-square statistic for the log rank test.

Results: Age at diagnosis ranged from 16 to 81 years (median: 44 years). The extremities were involved in 91 cases, the retroperitoneum in 3 cases, and the perineum in 1 case. The single most common location was the thigh (61 cases). Histologically, round cell differentiation was present in 41 cases (43%) ranging from 5% to 100% of the tumor volume. Only one case of "pure" RCL was used in the study. Spontaneous tumor necrosis was noted in 4 cases. By flow cytometry, 38 tumors were diploid, 6 were aneuploid, and 1 was tetraploid. The data from 1 case was uninterpretable. Thirty patients (35%) developed metastasis; 27 (31%) died from the disease.

Conclusions: With multivariate analysis, age ( > 45 years), percent of round cell differentiation ( > or = 25%), and the presence of spontaneous tumor necrosis are significantly associated with a poor prognosis. No correlation was observed between DNA ploidy (i.e., diploid vs. aneuploid) and percent of round cell differentiation or clinical outcome.