Liposarcoma arising in uterine lipoleiomyoma: a report of 3 cases and review of the literature.

BACKGROUND: Primary sarcomas of the uterus are uncommon, leiomyosarcoma being the most frequent. Most uterine sarcomas arise de novo, with malignant transformation of a benign mesenchymal tumor being a very rare event, and is reported only in leiomyomata.
DESIGN: The clinicopathologic features of 3 uterine liposarcomas arising in association with a lipoleiomyoma were studied. Immunohistochemistry for desmin, h-caldesmon, S100, and MDM2, and fluorescence in situ hybridization for the t(12;16) (q13;p11) were performed in all cases. RESULT: Patients ranged in age from 49 to 70 (mean, 59) years. The tumors were centered in the myometrium, ranged in size from 10 to 18.5 cm, and showed a gelatinous cut surface with foci of necrosis. On microscopic examination, the tumors had well-circumscribed pushing margins. One neoplasm was uniformly hypocellular with a prominent myxoid background, and a striking delicate vascular network. Another neoplasm showed alternating hypocellular (myxoid) and hypercellular areas, whereas the third tumor was uniformly hypercellular with a hyalinized background. In the myxoid areas, the cells were small and spindle with oval nuclei and inconspicuous nucleoli. In the hypercellular areas, the cells were pleomorphic with large, hyperchromatic nuclei. Mitotic activity ranged from <3 to 7/10 high-power fields. Lipoblasts were present in all tumors but were more common in the hypercellular areas. Two tumors merged imperceptibly with a lipoleiomyoma (1 typical and 1 with bizarre nuclei), whereas the third tumor showed an infarcted area composed of ghost mature adipocytes admixed with hyalinized smooth muscle most consistent with an infarcted lipoleiomyoma. Tumors were classified as myxoid, mixed myxoid and pleomorphic, and pleomorphic liposarcoma, respectively. The benign and malignant adipose components were positive for S100, whereas the benign smooth muscle component stained for desmin and h-caldesmon. MDM2 immunostain was positive in the 2 cases with a pleomorphic liposarcoma component. Fluorescence in situ hybridization analysis was successfully completed in only 1 of 3 tumors (pure pleomorphic liposarcoma), which failed to show the t(12;16) and HMAG2 amplification. The patients are alive and well 1, 2, and 20 years after initial surgery with no adjuvant therapy.
CONCLUSIONS: Primary liposarcomas of the uterus are extremely rare and are most likely to arise from malignant transformation of a lipoleiomyoma. These tumors should be added to the differential diagnosis of benign lipomatous tumors, myxoid mesenchymal tumors, and malignant mixed Müllerian tumors (if pleomorphic) of the uterus.