A 58-year-old woman was admitted to a hospital with pain in the upper right abdomen lasting for over 3 months. Laboratory tests for liver function and tumor markers were unremarkable. Contrast-enhanced computed tomography showed a 1.6 cm × 1.3 cm tumor on the arterial phase (Figure 1A). The mass seemed to be hepatocellular carcinoma, so the patient underwent partial hepatectomy (Figure 1B). Postoperative examination showed that the tumor consisted of thick-walled blood vessels and epithelioid myocytes, with no fatty component (Figure 1C and 1D). Further examination revealed positive immunostaining for melanocytic human melanin black-45 (HMB-45), desmin, and smooth muscle actin (Figure 1E–1G). Besides, Ki-67 immunohistochemical labeling index was about 1% to 2% (Figure 1H). These results confirmed that the patient had hepatic perivascular epithelioid cell neoplasm (PEComa). Five days after the surgery, the patient was discharged home, and regular follow-up examinations for 36 months have so far revealed no recurrence of hepatic PEComa.

Figure 1. A – contrast-enhanced computed tomography showing a 1.6 cm × 1.3 cm tumor in the right lobe of the liver (circle) before surgery, with marked enhancement in the arterial phase; B – surgical specimen of perivascular epithelioid cell neoplasm with a round, yellow mass with a clear margin. C, D – hematoxylin and eosin staining, magnification × 100 (C) and × 200 (D). The tumor consisted of thick-walled blood vessels and epithelioid myocytes, with no fatty component. Immunohistochemical staining for human melanin black-45 (E), desmin (F), and smooth muscle actin (G) were positive (magnification × 200). H – Ki-67 immunohistochemical labeling index of about 1% to 2% (magnification × 200)

The World Health Organization defines PEComa a rare disease in the form of “a mesenchymal tumor composed of histologically and immunohistochemically distinct perivascular epithelioid cells.”1 Hepatic PEComas have been described in only a few dozen cases, and are usually diagnosed incidentally.2 However, due to a lack of specificity in clinical presentation, laboratory tests, and imaging examinations, it is difficult to preoperatively distinguish hepatic PEComa from other types of liver tumors. The diagnosis of hepatic PEComa depends on histologic confirmation, in which immunohistochemical detection of HMB-45, melanoma antigen, and smooth muscle markers (actin and desmin) is characteristic and decisive.2

Surgical resection is a gold standard for treatment of hepatic PEComa,3 especially for patients who meet 2 or more of the following criteria: 1) tumor size above 5 cm, 2) infiltrative margins, 3) high-grade nuclear atypia, 4) mitotic count above 1/50 high-power fields, 5) hypercellularity, 6) vascular invasion, and 7) necrosis.4 Although most reported cases have a benign course, some are aggressive with locoregional recurrences and distant metastases.5 Therefore, long-term periodic follow-up is necessary.