"Fat-rich" (Spindle Cell-poor) Variants of Atypical Spindle Cell Lipomatous Tumors Show Similar Morphologic, Immunohistochemical and Molecular Features as "Dysplastic Lipomas" Are They Related Lesions?
Abstract
We appreciated the interest of Dr Creytens et al in our recent publication on dysplastic lipoma.1 This tumor has: (1) a very strong male predominance, (2) a predilection for the posterior neck, upper back and shoulder regions, (3) multifocality in TILDE OPERATOR+D9119% of patients, (4) a rare association with retinoblastoma, and (5) mildly increased risk (currently estimated at around 10%) for local recurrence with simple excision, as compared with a conventional lipoma. To date, all examples have been subcutaneous, though some examples have occurred in locations were tissue planes are somewhat ambiguous (eg, the lateral/anterior neck and groin regions). The key histologic features are: (1) notable adipocytic size variation, (2) patchy (typically single cell) fat necrosis, and (3) focal adipocytic nuclear atypia. The atypical adipocytes may be mononucleated or multinucleated. The atypia is generally mild and can be quite subtle, but in some instances, it is more pronounced and similar to that seen in a conventional atypical lipomatous tumor. Immunohistochemical expression for p53 is always present, but it is limited to a subpopulation of the adipocytes, typically those with the greatest atypia. MDM2 immunoexpression can be present, but it is almost invariably less prominent than the p53 immunoexpression, and FISH analysis for MDM2 gene amplification is always negative.