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MDM2-Positive Atypical Lipomatous Neoplasm/Well-Differentiated Liposarcoma Versus Spindle Cell Lipoma of the Orbit

Purpose: To distinguish, in a 36-year-old man, an atypical lipomatous neoplasm/well-differentiated liposarcoma from a spindle cell lipoma in a recurrent orbital tumor. Methods: Clinical, radiographic, and histopathologic evaluations coupled with immunohistochemical studies for CD34, factor XIII, bcl-2, S-100, muscle-specific actin, Ki-67, and MDM2. Results: MDM2 gene amplification was discovered in the CD34+ tumor cells. An average Ki-67 proliferation index of 28% was ascertained for the original and recurrent lesions. These findings established the diagnosis of a well-differentiated liposarcoma with lipoma-like and spindle cell features and ruled out a spindle cell lipoma. Conclusion: Well-differentiated liposarcoma is a slow growing, infiltrative, and nonmetastasizing neoplasm that is microscopically and diagnostically challenging. It can be reliably separated from a benign spindle cell or an atypical lipoma by using the markers MDM2 and Ki-67.