Table 1 Classification of malignant potential for non-gynecologic PEComas (adapted from [12])

(1) Size > 5 cm

(2) Infiltrative growth pattern

(3) High nuclear grade and cellularity

(4) Mitotic Rate > 1/50 HPF

(5) Necrosis

(6) Vascular invasion

• “Benign”: < 2 high risk features and size < 5 cm

• “Uncertain malignant potential”: Size ≥ 5 cm with no other high risk features OR nuclear pleomorphism/multinucleated giant cells only

• “Malignant”: ≥ 2 high risk features