Microscopic description and IHC:
The tumor is composed of epithelioid to spindled cells that appear to arrange around blood vessels. The cells have clear to granular eosinophilic cytoplasm; round to oval nuclei with small nucleoli. Malignant features are present, such as infiltrative growth, nuclear atypia, and atypical mitotic figures.
Immunohistochemistry shows that the tumor is positive for Caldesmon, SMA (focal), Desmin (focal), MiTF, Melan-A and HMB45 (weak), and negative for CK7, CK20, CD34, EMA, CAM5.2, AFP, CEA, TTF1, HMWK, S100, CD117, Hepatocyte, DOG1, PAX8, WT1, CD10, CDX2, Synaptophysin and Chromogranin. The epithelioid cells show more reactivity to melanocytic markers, whereas the spindled cells to muscle markers.
In addition, the patient’s arm lesion is also proved to be PEComa by FNA.
Discussion:
Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal neoplasms which can arise from almost any location in the body and includes angiomyolipoma (AML), clear cell “sugar” tumor of lung (CCST), lymphangiomyomatosis (LAM), clear cell myomelanocytic tumor of falciform ligament/ligamentum teres (CCMMT).
The unique feature of these tumors is the coexpression of muscle and melanocytic markers. These are identified immunohistochemically by the expression of Human Melanin Black-45 (HMB-45), Melan-A and Smooth Muscle Antigen (SMA) which are seen in the majority of PEComas.
The liver is uncommonly associated with PEComa and the approach to a patient with hepatic PEComa is not well described. There is no consensus regarding the neo-adjuvant/adjuvant therapy in these patients.
PEComa in the liver may mimic primary hepatic neoplasms such as hepatocellular carcinoma (conventional and fibrolamellar variant, positive for hepatocellular markers); and non-hepatic neoplasms such as metastatic leiomyosarcoma (negative for melanocytic markers), melanoma (negative for muscle markers), and gastrointestinal stromal tumor (GIST, positive for DOG-1, CD117).
References:
Folpe AL, Kwiatkowski DJ. Perivascular epithelioid cell neoplasms: pathology and pathogenesis. Hum Pathol 2010 Jan;41(1):1–15.
Bonetti F, Pea M, Martignoni G, Zamboni G. PEC and Sugar. Am J Surg Pathol. 1992;16:307–308. doi: 10.1097/00000478-199203000-00013
Lan YZ, Hua XE. Hepatic multiple perivascular epithelioid cell neoplasm: A case report and literature review. Molecular and clinical oncology 4: 619-621, 2016