Answer: C - Perivascular epithelioid cell tumor (PEComa)

The liver biopsy is composed of two distinct morphological areas. One area is composed of sheets of epithelioid cells with round to oval nuclei without prominent nucleoli and a modest amount of eosinophilic to clear ("ballooned") cytoplasm. Scattered thin-walled vessels are seen with occasional impingement by tumor cells. A separate area consists of clusters of foamy histiocytes/macrophages (confirmed by a CD68 immunostain). The morphologic differential diagnosis of the former region includes hepatocellular adenoma/carcinoma (with steatohepatitic features), metastatic renal cell carcinoma and PEComa. Immunostains show the tumor cells to be negative for CAM5.2, arginase-1, and PAX-8; they are positive for MelanA, HMB-45, and SMA (note the lack of immunostaining in the macrophage-rich region). The histomorphologic and immunophenotypic profile supports a diagnosis of perivascular epithelioid cell tumor (PEComa). 

PEComas, also known as angiomyolipoma or clear cell "sugar" tumor, can be primary in the liver and are composed of 3 cell types (with varying proportions): smooth muscle, fat and blood vessels. Approximately half of tumors lack a significant fat component. No adipocytes are noted in this biopsy, however macrophages may contain lipid from adjacent fat. PEComas are distinguished by their expression of both myoid and melanocytic markers. They may be sporadic or associated with tuberous sclerosis complex, although both presentations may be linked to mutations in TSC2. Although most cases have a benign clinical course, rare cases may be locally aggressive or become metastatic.