Ewing sarcoma/primitive neuroectodermal tumor (EWS/PNET) is a diagnostically challenging malignant round cell tumor with signature translocations involving the EWS gene. These translocations are detectable with both reverse transcriptase-polymerase chain reaction (RT-PCR) and fluorescence in situ hybridization (FISH) in formalin-fixed paraffin-embedded tissue. However, RT-PCR is less sensitive in formalin-fixed paraffinembedded than frozen tissue. Similarly, commercial FISH probes have recently become available, but have yet to be rigorously tested in the clinical setting. Therefore, we have compared RT-PCR with FISH using 'home brew' fusion probes for Ewing sarcoma (EWS)-FLI1 and a commercial EWS break apart probe set in 67 archival round cell tumors, including 27 EWS/PNETs. Sensitivities and specificities for both FISH assays were 91 and 100%, respectively, whereas RT-PCR had a sensitivity of 54% and a specificity of 85%. The break apart strategy was easier to interpret than probe fusion approach. We conclude that FISH is a more sensitive and reliable ancillary technique than RT-PCR for the diagnosis of EWS/PNET in formalin-fixed paraffin-embedded tissue, although the latter provides additional information regarding fusion transcript subtype and prognosis. The commercial break apart probe set is both readily available and easy to interpret, making it particularly attractive. Nonetheless, complex round cell tumors often benefit from molecular testing with multiple methods.

Aneurysmal bone cyst is a benign, cystic lesion of bone composed of blood-filled spaces separated by fibrous septa. Relatively few cases of aneurysmal bone cyst have been cytogenetically characterized, yet abnormalities of the short arm of chromosome 17 appear to be recurrent. In this study, conventional cytogenetic analysis of 43 aneurysmal bone cyst specimens from 38 patients over a 12-year period revealed clonal chromosomal abnormalities in 12 specimens. Karyotypic anomalies of 17p, including a complex translocation and inversion, were identified in eight of these 12 specimens. In an effort to further define the aberrant 17p breakpoint, fluorescence in situ hybridization (FISH) analyses were performed using a series of probe combinations spanning a 5.1 Mb region between the TP53 (17p13.1) and Miller-Dieker lissencephaly syndrome (17p13.3) gene loci. These studies revealed the critical breakpoint locus at 17p13.2, flanked proximally by an RP11-46I8, RP11-333E1, and RP11-457I18 bacterial artificial chromosome (BAC) probe cocktail and distally by an RP11-198F11 and RP11-115H24 BAC and RP5-1050D4 P1 artificial chromosome (PAC) probe cocktail. Overall, abnormalities of the 17p13.2 locus were identified by metaphase and/or interphase cell FISH analysis in 22 of 35 (63%) aneurysmal bone cyst specimens examined including 26 karyotypically normal specimens. These cytogenetic and molecular cytogenetic findings expand our knowledge of chromosomal alterations in aneurysmal bone cyst, further localize the critically involved 17p breakpoint, and provide an alternative approach (ie FISH) for detecting 17p abnormalities in nondividing cells of aneurysmal bone cysts. The latter could potentially be utilized as an adjunct in diagnostically challenging cases.

Background: Cytogenetic studies of malignant peripheral nerve sheath tumours (MPNSTs) and malignant triton tumours (MTTs) are rare. Aims: To undertake cytogenetic analysis of these tumours. Methods: Conventional cytogenetic analysis of 21 MPNSTs and MTTs from 17 patients (nine with peripheral neurofibromatosis (NF1)) was carried out using standard culture and harvesting procedures.For a more precise identification of composite structural rearrangements and marker chromosomes, spectral karyotypic analysis (SKY) was applied to a subset of cases. In addition, EGFR gene copy number was assessed by fluorescence in situ hybridisation (FISH) analysis in a subset of cases. Results: Cytogenetic analysis revealed predominantly complex karyotypes. SKY analysis was useful in further defining many structural anomalies. Structural aberrations most frequently involved chromosomal bands or regions 1p31-36, 4q28-35, 7p22, 11q22-23, 19q13, 20q13, and 22q11-13. Overall, loss of chromosomal material was much more common than gain. Loss of chromosomes or chromosomal regions 1p36 (48%), 3p21-pter (52%), 9p23-pter (57%), 10 (48%), 11q23-qter (48%), 16/16q24 (62%), 17(43%), and 22/22q (48%), and gains of 7/7q (29%) and 8/8q (29%) were most prominent. These gains and losses were distributed equally between MPNST and MTT, demonstrating that these entities are similar with respect to recurrent genomic imbalances. Similarly, none of the recurrent chromosomal breakpoints or imbalances was restricted to either NF1 associated or sporadic MPNSTs. FISH analysis was negative for amplification. Conclusions: These cytogenetic and molecular cytogenetic findings expand the knowledge of chromosomal alterations in MPNST and MTT, and point to possible recurring regions of interest.

Adamantinoma of long bones is a rare low-grade malignant bone tumor most often arising in the tibia, but also occasionally exhibiting synchronous involvement of the ipsilateral fibula. Some adamantinomas have "osteofibrous dysplasia-like" features. 1 Thus, a relationship between adamantinoma and osteofibrous dysplasia (a benign fibro-osseous lesion occurring almost exclusively in the tibia of children less than 10 years of age) has been proposed. This relationship, however, is poorly understood.Cytogenetic analyses of adamantinoma and osteofibrous dysplasia are few. [2][3][4][5][6][7] In this study, the cytogenetic and molecular cytogenetic findings of four cases of adamantinoma and a review of the literature are presented. Materials and Methods Case 1A 37-year-old female presented with a nontender protuberance in the midshaft of the right tibia known since childhood. As a child, she sustained a fracture of the tibia with minimal trauma. The fracture was treated in a cast and healed without complications. For 20 years, the protuberance remained unchanged in size and character and without symptoms. In 1999, however, she sustained a fracture of the tibia once again and with minimal trauma. Plain radiographs demonstrated a pathological fracture through a destructive process including the lesion and protuberance. A biopsy revealed adamantinoma. A radical en bloc resection of the right tibial diaphysis and reconstruction using fresh frozen allograft tibia, plates, and autologous bone graft were performed.Histopathologically, both the biopsy and resected specimens were composed of epithelial-like cells arranged in large islands or nests embedded in a densely fibrous stroma. Mitotic figures could not be identified. Immunohistochemical staining revealed that the epithelial cells were immunoreactive for cytokeratin (AE1:AE3). The histopathological diagnosis was classic adamantinoma. Case 2A 20-year-old male sought medical attention because of pain in the anterior aspect of his right leg with recreational running. Four years earlier, the patient had noted a bulge on the anterior border of his right tibia. Plain radiographs revealed a bubbly lesion involving the anterolateral cortex of the midshaft of the right tibia. Comparison with previous radiographs over the past 4 years showed indolent progression (Figure 1). Magnetic resonance imaging (MRI) demonstrated a multilobulated mass that uniformly enhanced with contrast. A bone scan showed intense uptake confined to the site of the lesion seen in the plain radiographs and revealed no other areas of significant skeletal uptake. An incisional biopsy was followed by a wide local excision and reconstruction.Microscopically, the lesional tissue was intracortical. At the periphery, the cortex demonstrated enlarged Harversian canals filled with a paucicellular fibroblastic reactive tissue. There was a transition from mature to less mature bone tissue, or so-called zoning. The center of the lesion