Pathology: perivascular epithelioid cell tumour (PEComa)

Angiomyolipoma

• Sheets of adipocytes with interspersed nests and fascicles of spindle cells 

• Adipocytes have abundant clear cytoplasm with occasional vacuolation; small eccentric nuclei

• Spindle cells have eosinophilic cytoplasm; monomorphic ovoid nucleoli with small nucleoli and inconspicuous mitotic activity

• Interspersed is a prominent ectatic vasculature

• IHC: Melan-A

Angiomyolipoma

• Sheets of adipocytes with interspersed nests and fascicles of spindle cells 

• Adipocytes have abundant clear cytoplasm with occasional vacuolation; small eccentric nuclei

• Spindle cells have eosinophilic cytoplasm; monomorphic ovoid nucleoli with small nucleoli and inconspicuous mitotic activity

• Occasional ectatic vessels; central dollop of hyalinized collagen 

• IHC: HMB45, Melan-A

PEComa

History of tuberous sclerosis

• Anastomosing cords of epithelioid cells

• Amphophilic cytoplasm with indistinct cell borders

• Round-ovoid nuclei with prominent nucleoli and mild pleomorphism; inconspicuous mitotic activity

• Intersecting hyalinized fibrovascular septa

• IHC: smooth muscle actin, desmin, HMB45, Melan-A

PEComa, malignant

• Sheets and fascicles of spindle-epithelioid cells

• Eosinophilic cytoplasm with occasional clearing

• Ovoid nuclei with small nucleoli; mitotic activity

• Collagenous stroma; variably-sized blood vessels with perivascular neoplastic cells growth

• IHC: desmin, SMA, H-caldesmon, HMB45, Melan-A

• DNA-seq: TSC2 SNV (p.Q478*),  PTEN SNV (p.F341V)

PEComa, malignant

• Spindle cells in fascicles with rare nests of polygonal cells

• Granular eosinophilic-clear cytoplasm

• Ovoid nuclei; polygonal cells have hyperchromasia, multilobation and marked pleomorphism; mitotic activity

• Patchy necrosis

• IHC: Melan-A

• RNA-seq: TSC2 SNV (p.Q478)

PEComa

• Nests and anastomosing cords of epithelioid cells

• Abundant amphophilic cytoplasm

• Round-ovoid nuclei with vesicular chromatin, prominent nucleoli and mild pleomorphism; inconspicuous mitotic activity

• Intersecting fibrovascular septa

• IHC: Melan-A

PEComa

• Sheets of epithelioid cells

• Abundant amphophilic cytoplasm

• Round-ovoid nuclei with macronucleoli, moderate pleomorphism and occasional multinucleation; mitotic activity

• Prominent ectatic vasculature

• IHC: Melan-A

PEComa

• Sheets of epithelioid-spindle cells

• Abundant eosinophilic cytoplasm

• Round-ovoid nuclei with macronucleoli, moderate pleomorphism and occasional multinucleation; mitotic activity

• Occasional small ectatic vessels

• IHC: smooth muscle actin, Melan-A