Residency Program - Case of the Month
September 2013 - Presented by Michael Van Ness, M.D.
Paratesticular well-differentiated lipoma-like liposarcoma.
Paratesticular malignancies are rare. In adults more than 75% of these lesions arise from the spermatic cord. Most spermatic cord tumors are benign (70 to 80%) and are comprised primarily of lipomas. Liposarcomas are the second most frequent sarcoma in adults and reportedly represent approximately 3 to 7% of all spermatic cord sarcomas.
Spermatic cord liposarcoma usually presents as a painless scrotal swelling that grow in size slowly during a period ranging from months to years. Occasionally a previously stable mass can rapidly increase in size. Average patient age at presentation is 55 years with a slight right side preponderance. Less than 6% of cases have a history of scrotal surgery or trauma. Most authorities believe that liposarcomas arise from mesenchymal cells rather than from malignant transformation of lipomatous cells.
The histological differential diagnosis of well-differentiated lipoma-like liposarcoma consists of other benign fatty tumors, i.e., normal fat or simple lipomas. These can be excluded by the presence of atypical cells with large, hyperchromatic nuclei, either in the fibrous septa or in the fat. These cells can be very focal. Some cases additionally contain lipoblasts, however these are not essential for the diagnosis.
Distinguishing atypical lipomatous tumor-well-differentiated liposarcoma (WDL) from benign adipocytic neoplasms and dedifferentiated liposarcoma (DDL) from pleomorphic or myxoid liposarcoma (LPS) can be difficult. WDL and DDL characteristically harbor ring chromosomes, amplifications of the MDM2 and CDK4 cell cycle oncogenes with protein overexpression, and can also overexpress the cell cycle regulator p16.
The immunohistochemical trio of CDK4, MDM2, and p16 is a useful ancillary diagnostic tool that provides strong support in distinguishing WDLs from other adipocytic neoplasms with a sensitivity and specificity for detecting WDLs or DDLs of 71% and 98%, respectively. Of these three markers, p16 is the most sensitive and specific marker for WDL.
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