Atypical subcutaneous fatty tumors: a review of 37 referred cases.

We reviewed 37 referred, atypical, subcutaneous fatty tumors. There was a male preponderance (28:9). The median age was 51.5 years (26-83); the median duration of symptoms was 18 months (three weeks to 35 years); the median size was 5.5 cm (1.5-20) and the posterior cervico-dorsal areas (17 cases) was the commonest location. We divided tumors into five histological categories: (1) subcutaneous fibrolipomas with slight fibroblastic atypia (five cases); (2) subcutaneous spindle cell lipomas with atypia (mixed spindle cell/pleomorphic lipomas) without lipoblasts (three cases); (3) subcutaneous atypical well-differentiated fatty tumors (pure pleomorphic lipomas) without lipoblasts (nine cases); (4) subcutaneous atypical well-differentiated fatty tumors (pleomorphic lipomas) with lipoblasts (17 cases); (5) subcutaneous atypical fatty tumors with poorly differentiated or de-differentiated areas (three cases). Follow-up information was obtained in 25 cases (68%). The follow-up times were from three to 192 months (median 31). Five tumors (20%) recurred, two as the same and three as a higher histological category. Two were originally referred because of a recurrence. Four recurred once and one, initially a category 4 tumor, recurred twice as a category 5 tumor. Two category 1 and three category 4 tumors recurred. There were no recurrences in the other three groups. All recurrent tumors were located outside the cervico-dorsal areas. The sizes of two tumors that recurred were 2.8 and 3 cm and the time to first recurrence was from one to 85 months. Two recurrent tumors of high histological category were controlled by re-excision and either radiotherapy or combined chemotherapy and radiotherapy. This series suggests that atypical subcutaneous fatty tumors comprise a continuous and potentially transforming histological spectrum, which ranges from mildly atypical fibrolipomas through various mixed spindle cell and pleomorphic lipoma patterns to tumors indistinguishable from de-differentiated liposarcomas. Despite a sometimes alarming histological appearance, none in the present series metastasized.