A de novo unclassified malignant spindle cell neoplasm of liver allograft.

Spindle cell neoplasms are rarely reported in liver allografts; most are benign and associated with Epstein-Barr virus infection. We present a case of a malignant spindle cell neoplasm arising in a liver allograft. The patient underwent orthotopic liver transplant for cirrhosis secondary to nonalcoholic steatohepatitis. After 2 years, he presented with vague abdominal complaints. Imaging studies revealed a 10-cm right hepatic lobe mass. The patient underwent right-sided hepatectomy. The tumor displayed areas of broad, relatively hypocellular fascicles, whorls, and perivascular clustering; spindle cells with mild to moderate nuclear pleomorphism; and relatively abundant eosinophilic cytoplasm. Mitotic activity ranged from 2 to 4 mitotic figures per 20 high-power fields. Immunostaining displayed positivity for epithelial membrane antigen, vimentin, CD99, BCL2, cytokeratin, and human herpesvirus 8. Interphase fluorescence in situ hybridization findings were negative for a translocation involving the SS18 gene (18q11). We believe the tumor represents the first reported case of a novel unclassified spindle cell malignant neoplasm in a liver allograft.