Poorly differentiated malignant neoplasm showing a "BRD4-variant" translocation Sara O. Vargas, M.D. Department of Pathology, Children's Hospital Boston, MA

Case History: This previously healthy girl presented at age 23 months with a 3-day history of shortness of breath. Mild subcostal and intercostal retractions were observed. There were bronchovesicular breath sounds on the right side accompanied by inspiratory and expiratory wheezes. A 0.5-cm firm mobile subclavicular lymph node was palpable. Chest x-rays showed complete opacification of the right hemithorax and a left mediastinal shift, and a CT scan demonstrated a large mass in the right hemithorax and a pleural effusion. On hospital day #2, open biopsy and debulking were performed via median sternotomy, during which the tumor was noted to involve the right lung and encase the trachea. Within several days the patient developed superior vena cava (SVC) syndrome and increasing respiratory and ventilatory failure. On hospital day #9, she underwent an emergent tumor resection which included a right pneumonectomy, further mediastinal debulking, and a right pneumonectomy. Recrudescent growth led to recurrent SVC syndrome. Chemotherapy (ifosfamide, adriamycin, and vincristine), begun on hospital day #40, was complicated by pancytopenia, and in the setting of worsening ventilatory failure, the patient died on hospital day #49. An autopsy was declined. Microscopic features: Histologic sections showed a poorly differentiated neoplasm growing in nests, cords, and sheets with fine fibrous septa. In some areas the cells were closely packed with overlapping nuclei, while in other areas, there was a discohesive appearance. Nuclei were large and round with open vesicular chromatin and conspicuous nucleoli. Cytoplasm was scant and amphophilic. Mitosis and single-cell necrosis were frequent. Patchy confluent necrosis was also seen. Slide 1 Click to view with ImageScope Click to view with a Web-Based Viewer Immunostaining showed patchy positivity for desmin, faint nonmembranous positivity for CD99, and foci of possible faint staining for EMA. The following immunostains were negative: cytokeratins (MNF116, AE1/AE3, Cam5.2), WT-1, alk-1, PLAP, CD30, CD45, synaptophysin, chromogranin, PGP9.5, NB84, myogenin. Molecular studies: Cytogenetic analysis showed the following karyotype: t(10;19)(q22.3;p13.1). FISH on paraffin sections showed a rearrangement involving the gene BRD4 (at 19p13.1), but not NUT (at 15q13). Diagnosis: Poorly differentiated malignant neoplasm showing a "BRD4-variant" translocation. Comment: The case presented is that of a poorly differentiated malignant tumor with a chromosomal translocation that is a variant of that observed in "t(15:19) carcinoma." Tumors harboring the t(15;19) translocation have been recently identified as a particularly lethal subset of tumors affecting young patients and usually involving the upper respiratory tract or other midline structures. There is almost invariably a rapidly fatal clinical course, often with superior vena cava syndrome due to the tumor's rapid and bulky local growth. The tumors generally have the histologic appearance of undifferentiated or poorly differentiated carcinomas, often requiring ancillary techniques such as immunostaining or electron microscopy to demonstrate epithelial differentiation. Squamous differentiation may be perceptible in some cases and often becomes more apparent following chemotherapy. Only one case reported to date lacked epithelial differentiation altogether; this occurred in bone and was likened histologically to Ewing sarcoma. Distinguishing t(15;19) tumors from conventional carcinoma is not possible solely on histologic means. Although the occurrence of a poorly differentiated carcinoma in a child or young adult might raise suspicion, genetic confirmation is required; this can be done by conventional karyotype, by FISH using probes directed at the breakpoints, or by PCR. This pediatric carcinoma is distinctive in that it is characterized by relatively simple chromosomal rearrangements, as opposed to adult carcinomas, which presumably arise after multiple genetic insults often related to chronic environmental exposures and are generally characterized by extremely complex karyotypes. Pediatric tumors, most commonly sarcomas, tend to harbor single or few genetic changes, and thus have served as excellent entry points for uncovering genetic mechanisms of tumorogenesis. The identification of t(15;19) carcinoma is particularly noteworthy because it is the first aggressive carcinoma to be characterized by a translocation. The genes affected by the t(15;19) translocation have been identified as BRD4 (at 19p13) and NUT (at 15q13). BRD4 is a member of the bromodomain gene family, known from murine models to play a critical role in regulating cell cycle progression and cellular proliferation. Bromodomain-containing fusions have been demonstrated in several types of leukemia, including AML with t(8;16). The normal function of the gene NUT (named for nuclear protein in testis) is unknown. Its expression to date has been identified only in testis and in NUT-rearranged tumors, where it is localized in the nucleus. The oncogenic mechanism of BRD4-NUT fusion is currently a subject of intense investigation. Three cases of carcinoma showing NUT translocated with an unknown variant partner have been described. These may have a tendency toward better squamous differentiation and more prolonged survival. The case presented herein is the first observation of a "BRD4-variant" tumor. It appears similar to the spectrum of classic t(15;19) tumors in that it affected a young patient, involved the lung/mediastinum, exhibited a poorly differentiated morphology, and rapidly led to death. Immunostaining of the tumor presented herein helped to rule out other poorly differentiated "round cell" neoplasms of childhood such as Ewing sarcoma, lymphoma, and rhabdoid tumor. Another childhood neoplasm in the differential diagnosis is pleuropulmonary blastoma (PPB). PPB is an aggressive poorly differentiated intrathoracic neoplasm that most often presents as an extremely large mass in a child under age 5. Histologic components include primitive elements such as blastema and rhabdomyosarcoma. Primitive or malignant-appearing cartilage as well as fibrosarcomatous areas may also be apparent. Anaplasia is common. Benign epithelial cysts, presumed to represent maldeveloped underlying lung tissue, may be interspersed. Since its description in 1988, PPB has been increasingly recognized; it may now be that some pathologists are using this term as a diagnosis for a broad range of primitive neoplasms occurring in the lung. Some authors, for example, have advocated conceiving virtually every apparent embryonal rhabdomyosarcoma of the lung as PPB. But the spectrum of primary intrathoracic tumors with primitive features that should be designated PPB is not well defined. The lack of well-defined recurrent karyotypic abnormalities in tumors reported as PPB suggests that the published cases may represent a diverse grouping. The primitive tumor reported herein lacks the morphologic heterogeneity (i.e., rhabdomyosarcomatous elements, cartilage, anaplasia, spindled fibrosarcoma-like pattern) typical of many PPB. Its distinctive genetics set it apart and serve to illustrate that not all primitive primary neoplasms of the lung are PPB. As exemplified by the case presented herein, tumor genetics are becoming an important part of the field of pathology. This is especially true in the area of pediatric neoplasia, where characteristic genetic aberrations are a distinguishing feature of many pediatric tumors, and where pathologists are often confronted with primitive and poorly differentiated tumors in which genetic testing can be of particular aid diagnostically. Selected references: BRD4-NUT fusion tumors: French CA, Kutok JL, Faquin WC, Toretsky JA, Antonescu CR, Griffin CA, Nose V, Vargas SO, Moschovi M, Tzortzatou-Stathopoulou F, Miyoshi I, Perez-Atayde AR, Aster JC, Fletcher JA. Midline carcinoma of children and young adults with NUT rearrangement. J Clin Oncol 2004;22(:4135-9. French CA, Miyoshi I, Kubonishi I, Grier HE, Perez-Atayde AR, Fletcher JA. BRD4-NUT fusion oncogene: a novel mechanism in aggressive carcinoma. Cancer Res. 2003;63:304-7. French CA, Miyoshi I, Aster JC, Kubonishi I, Kroll TG, Dal Cin P, Vargas SO, Perez-Atayde AR, Fletcher JA. 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Hidden chromosomal abnormalities in pleuropulmonary blastomas identified by multiplex FISH. BMC Cancer 2006;6:4. Sciot R, Dal Cin P, Brock P, Moerman P, Van Damme B, De Wever I, Casteels-Van Daele M, Van Den Berghe H, Desmet V. Pleuropulmonary blastoma (pulmonary blastoma of childhood): genetic link with other embryonal malignancies? Histopathology 1994; 24:559-63. Vargas SO, Nose V, Fletcher JA, Perez-Atayde AR. Gains of chromosome 8 are confined to mesenchymal components in pleuropulmonary blastoma. Pediatr Dev Pathol 2001;4:434-45. Acknowledgements: These insights would be impossible without the efforts of Chris French, M.D., of Brigham and Women's Hospital, Boston , MA , whose outstanding laboratory work has resulted in the identification and characterization of the BRD4-NUT fusion. Dr. French performed the FISH in this case. Thanks to the referring pathologist, Edith F. Schmidt, M.D., of Laboratory Medicine Consultants, Las Vegas, NV for providing material and detailed clinical records for the patient presented herein. And thanks to Stephen J. Qualman, M.D., and the Children's Oncology Group for the opportunity to review material from primary pediatric tumors archived in the Biopathology Center , Columbus , OH .