A variety of malignancies have been reported to arise within congenital melanocytic nevi, most commonly malignant melanoma, but rarely rhabdomyosarcoma, liposarcoma, and malignant peripheral nerve sheath tumor as well. There have been only three documented cases of rhabdomyosarcoma arising within congenital melanocytic nevi: two embryonal rhabdomyosarcomas and one mixed liposarcoma and rhabdomyosarcoma. One of these cases was also associated with neurocutaneous melanosis. We report a fourth case of rhabdomyosarcoma originating from a congenital melanocytic nevus. A 4-year-old girl presented with a large ulcerated nodule that developed within a hairy congenital nevus on her left gluteal and sacral regions. Her parents refused postoperative adjuvant therapy, and she died 13 months after surgical excision. Histologic sections showed a lesion with two distinct components. There was an expansile proliferation of pleomorphic cells within a fibromyxoid stroma. The neoplastic cells were spindled, and some had abundant eosinophilic globular cytoplasm with occasional cross-striations characteristic of rhabdomyoblasts. They strongly expressed desmin and myoglobin and were negative for S-100 protein and HMB-45. The tumor merged with an adjacent congenital melanocytic nevus characterized by a proliferation of uniform nonatypical melanocytes. The finding of both rhabdomyoblastic and melanocytic differentiation within the same lesion lends support to the hypothesis of their derivation from common pluripotential stem cells or neural crest cells.

Three uterine tumors, each consisting of endometrioid carcinoma and Ewing's sarcoma/peripheral primitive neuroectodermal tumor (ES/pPNET) are described. The diagnosis of ES/pPNET in each case was first established in the hysterectomy specimen because each ES/pPNET was misinterpreted on the endometrial biopsy specimens as a high-grade homologous sarcoma. The ES/pPNET element in each case consisted of solid masses of small- to medium-sized round cells without Homer-Wright pseudorosettes, glial or ganglion cells, true rosettes with central lumens, or medulloepithelial tubules. Each ES/pPNET exhibited focal positive immunostaining for neuron-specific enolase, diffuse staining for vimentin, and strong cell membrane immunoreactivity for O13 (CD99), the last finding providing the first clue to the diagnosis of ES/pPNET in each case. The diagnosis in each case was confirmed by detection of EWS/FLI-1 fusion transcript through reverse transcription polymerase chain reaction. We also examined O13 immunoreactivity retrospectively in 40 cases of malignant mixed mullerian tumors (MMMT) with homologous or heterologous elements. O13 immunoreactivity was not observed in the malignant epithelium or in the homologous or heterologous sarcomas. The immunoreactivity of O13 in round cell endometrial sarcomas provides a clue to the diagnosis of ES/pPNET.

We report a case of juxtaposed atypical meningioma and meningioangiomatosis (MA) in an 8-year-old boy with no clinical stigmata or family history of neurofibromatosis. We studied the proliferative activity and genetic changes in the two lesions in an attempt to define their biologic and pathogenetic relationships. The MIB-1 index was 11% in the meningioma and <1% in the MA, indicating increased proliferative activity in the meningioma. Fluorescence in situ hybridization was done for two chromosomal regions commonly deleted in meningiomas. There was loss of the neurofibromatosis 2 locus (22q12) in both the meningioma and MA. Conversely, the region of 1p32 was not deleted. Our results indicate that both the meningioma and MA arose from the same clonal process, with the meningioma probably undergoing additional, but undefined, genetic alterations that confer upon it a more proliferative potential. This loss of 22q12 in the MA raises doubt about the presumed hamartomatous nature of MA.

A variable proportion of bile duct adenomas of the liver are still confused with metastatic well-differentiated adenocarcinoma by surgeons and pathologists. We present here three examples of previously undescribed primary hepatic bile duct tumors that were composed almost entirely of clear cells that closely mimicked metastatic renal cell carcinoma. They were interpreted as atypical bile duct adenomas and occurred in two males and one female whose ages ranged from 25 to 64 years. All three tumors were incidental findings and measured from 0.8 to 1.1 cm. The clear neoplastic cells showed mild nuclear atypia and no mitotic activity. They were arranged in tubules and nests that focally infiltrated the hepatic parenchyma. For comparison, a case of clear cell cholangiocarcinoma and 13 conventional bile duct adenomas were examined. The clear cell cholangiocarcinoma was larger (6.0 cm) and had the tubular pattern of conventional cholangiocarcinoma and an abundant desmoplastic stroma. The clear cells of this tumor exhibited greater nuclear atypia and increased mitotic activity. All three atypical bile duct adenomas expressed cytokeratin (CK) 7, p53 protein, epithelial membrane antigen (EMA), and carcinoembryonic antigen (CEA); they were negative for CK20, vimentin, Hep Par 1, chromogranin, and prostatic specific antigen (PSA) and exhibited less than 10% of Ki-67-positive nuclei. One atypical bile duct adenoma displayed luminal immunoreactivity for villin. With the exception of Ki-67 reactivity, the 13 conventional bile duct adenomas and the clear cell cholangiocarcinoma had essentially a similar immunohistochemical profile as that of the atypical clear cell bile duct adenomas. The absence of an extrahepatic primary tumor, the histologic features, the immunohistochemical profile, and the fact that all patients are symptom-free 2 months to 18 years after wedge liver biopsy support the interpretation of atypical clear cell bile duct adenoma. The differential diagnosis with clear cell hepatocellular carcinoma and metastatic clear cell carcinomas is discussed.