Atypical spindle cell/pleomorphic lipomatous tumor: A clinicopathologic, immunohistochemical, and molecular study of 20 cases

Abstract

Lipomatous tumors accompanied by spindle cell component are not frequently encountered, and there are still problems regarding their differential diagnosis, nature, and nomenclature. To contribute to ongoing efforts, we present the clinical, histologic, and immunohistochemical characteristics of 20 cases of spindle cell lipomatous tumors with atypical features that may also be called atypical spindle cell/pleomorphic lipomatous tumors. Of the patients, 13 were men and 7 were women with an average age of 57.5 years. The most commonly affected site was the extremities. Twelve tumors arose in the subcutaneous tissue, while eight cases were located in the deep soft tissues. Tumor margins were often ill-defined with invasion into the surrounding tissues. Microscopic examination revealed a wide spectrum of histologic features. All cases consisted of poorly marginated proliferation of mildly atypical spindle cells set in a fibrous or myxoid stroma with a variable amount of adipocytic component showing variation in adipocyte size and scattered nuclear atypia and frequent univacuolated or multivacuolated lipoblasts. Tumor cellularity and the relative proportion of the components were highly variable. One tumor showed morphologic features evocative of dedifferentiation and another one exhibited histological features resembling pleomorphic liposarcoma. None of the patients had recurrence or metastasis at follow-up.

An atypical pleomorphic lipomatous tumor arising on the cheek

“…Most recently, Bahadir et al described a similar neoplasm, terming it atypical spindle cell/pleomorphic cell lipomatous tumor (ASCPLT). They reported 20 cases, all of which expressed CD34+ but were negative for MDM2, S100, and RB1.…”

Atypical Pleomorphic Lipomatous Tumor

“…whereas nuclear MDM2 expression is absent. Nuclear Rb expression is deficient in all published cases (Creytens et al 2017;Bahadır et al 2018).…”

“…The real incidence of atypical pleomorphic lipomatous tumor is difficult to assess, as most of our knowledge of this very recently described entity is based on small series or single case reports (Creytens et al 2017(Creytens et al , 2019Bahadır et al 2018;Boyd 2019).…”

“…Atypical pleomorphic lipomatous tumor occurs predominantly in middle-aged adults with a peak incidence in the seventh decade of life but can affect patients of any age (cases have been described in cases from 28 to 84 years old) (Creytens et al 2017;Bahadır et al 2018).…”

“…Atypical pleomorphic lipomatous tumors arise in the subcutis slightly more frequently than in deep (subfascial) somatic soft tissues and only occasionally arise in purely intradermal, intracavitary, or visceral locations. The anatomic distribution is wide, predominating in the limbs and limb girdles (Creytens et al 2017, Mariño-Enriquez et al 2017Bahadır et al 2018;Boyd 2019).…”