Clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres- A novel member of the perivascular epithelioid clear cell family of tumors with a predilection for children and young adults

The perivascular epithelioid cell family of tumors (PEComas), defined by th eir co-expression of melanocytic and muscle markers, includes angiomyolipom a, lymphangioleiomyoma, and clear cell "sugar" tumors of the lung, pancreas , and uterus. We present seven cases of a unique and previously unrecognize d tumor of children and young adults, which represents a new addition to th e PEComa group of tumors. Culled from three institutions over a 50-year per iod, all cases occurred in or immediately adjacent to the ligamentum teres and falciform ligament. Six patients were female and one male; their ages r anged from 3 to 21 years (median, 11 yrs). Tumor sizes ranged from 5 to 20 cm (median, 8 cm), All cases consisted of clear to faintly eosinophilic spi ndled cells arranged in fascicular and nested patterns. The cells had small but distinct nucleoli and low mitotic activity. Immunohistochemically, all cases were positive with antibodies to gp100 protein (HMB-45) and negative for 5-100 protein. In three of the seven cases studied immunohistochemical ly, the tumors expressed smooth muscle actin, melan-A, microphthalmia trans cription factor (MiTF), and myosin, but not desmin, No expression of the TS C2 gene product, tuberin, was seen in three cases. One case studied cytogen etically disclosed a t(3;10). Follow-up data, available in six of seven cas es (median duration, 18 mos), showed five patients to be free of disease an d one to have a radiographically presumed lung metastasis. We think these t umors comprise a new entity for which we propose the term "clear cell myome lanocytic tumor of the falciform ligament/ligamentum teres." The differenti al diagnosis of these tumors includes clear cell sarcoma of tendons and apo neuroses, leiomyosarcoma, and angiomyolipoma.