“LOW-FAT” MYXOID SPINDLE CELL LIPOMA MIMICKING A MYXOMATOUS LESION: CASE REPORT AND IMMUNOHISTOCHEMICAL ANALYSIS

Abstract

Spindle cell lipoma (SCL) and pleomorphic lipoma (PL) constitute a spectrum of lipomatous lesions with distinctive clinicopathologic features. Multiple variants of SCL/PL have been reported including fibrous, plexiform, vascular, pseudoangiomatous, low-fat/fat-free, and myxoid changes. Herein we present a case of a 1 cm submucosal nodular lesion excised from the buccal mucosa of a 55-year-old female patient with classic histopathologic and immunohistochemical features of “low-fat” SCL with prominent myxoid stroma that initially suggested soft-tissue myxomatous lesion other than SCL. The current case exhibited microscopically few adipocytes supported by exuberant myxoid stroma. Immunohistochemistry was positive for CD34, vimentin, CD10 (on the spindle cells and myxoid component), as well as for S100 (on adipocytes). The Ki-67 was <1%. Pan-cytokeratin (AE1/AE3), desmin, a-SMA, EMA, bcl-2, p53 and remarkably retinoblastoma protein (pRb), were negative. “Low-fat” myxoid SCL bear no significant clinical/prognostic, but they pose a diagnostic challenge to pathologists who may be unfamiliar with this variant.