Low-fat and fat-free pleomorphic lipomas: a diagnostic challenge.

Pleomorphic lipomas are benign tumors that most commonly present as subcutaneous masses in the head and neck, shoulder, or back region of middle-aged to elderly men. They are related to spindle cell lipomas based on shared cytogenetic aberrations and histologic features. When little or no fat is present, the diagnosis can be challenging. A review of 38 pleomorphic lipomas seen in consultation revealed 7 cases in which fat was present in reduced (<5%) amounts (n = 5) or absent (n = 2). Six of 7 cases were from men with a mean age of 59 years. Excluding 1 case where the site was not specified, they all presented as solitary well-circumscribed subcutaneous masses in the head and neck (n = 3) or shoulder (n = 2) region. The seventh case was an intradermal tumor from the nose of a 48-year-old woman. All displayed pleomorphic and multinucleated floret cells interspersed among bland spindle cells and ropey collagen. They were diffusely immunoreactive for CD34. Referring diagnoses, when provided, included myxofibrosarcoma, giant cell fibroblastoma, and granulomatous rosacea for the tumor from the nose; none considered pleomorphic lipomas. When fat is absent or present in reduced amounts, clinical context and identification of classic nonlipogenic components are essential for the diagnosis of pleomorphic lipomas.