|The histologic features of PEComa vary from a predominantly spindled morphology with cells arranged in short fascicles and cell nests to a predominantly epithelioid morphology arranged in a nested or sheet-like pattern. A prominent intrinsic vasculature is almost always present, ranging from an extensive, arborizing capillary network to thick-walled, often hyalinized larger caliber vessels. All PEComas express at least one melanocytic marker, with HMB-45 most frequently expressed (92%), followed by Melan-A (72%), and MiTF (50%).
Folpe et al have classified PEComas into "benign," "uncertain malignant potential," and "malignant" categories based on tumor size (> 5 cm); infiltrative margins; high grade nuclear atypia and cellularity; mitotic index (> 1 MF/50 HPF); necrosis; and vascular invasion.
Folpe AL, Mentzel T, Lehr HA, et al. Perivascular epithelioid cell neoplasms of soft tissue and gynecologic origin: a clinicopathologic study of 26 cases and review of the literature. Am J Surg Pathol 2005;29:1558-1575.