Aidan McManus

Detection of the PAX3-FKHR fusion gene in paediatric rhabdomyosarcoma: a reproducible predictor of outcome?

Rhabdomyosarcoma has 2 major histological subtypes, embryonal and alveolar. Alveolar histology is associated with the fusion genes PAX3-FKHR and PAX7-FKHR. Definition of alveolar has been complicated by changes in terminology and subjectivity. It is currently unclear whether adverse clinical behaviour is better predicted by the presence of these fusion genes or by alveolar histology. We have determined the presence of the PAX3/7-FKHR fusion genes in 91 primary rhabdomyosarcoma tumours using a combination of classical cytogenetics, FISH and RT-PCR, with a view to determining the clinical characteristics of tumours with and without the characteristic translocations. There were 37 patients with t(2;13)/PAX3-FKHR, 8 with t(1;13) PAX7-FKHR and 46 with neither translocation. One or other of the characteristic translocations was found in 31/38 (82%) of alveolar cases. Univariate survival analysis revealed the presence of the translocation t(2;13)/PAX3-FKHR to be an adverse prognostic factor. With the difficulties in morphological diagnosis of alveolar rhabdomyosarcoma on increasingly used small needle biopsy specimens, these data suggest that molecular analysis for PAX3-FKHR will be a clinically useful tool in treatment stratification in the future. This hypothesis requires testing in a prospective study. Variant t(1;13)/PAX7-FKHR appears biologically different, occurring in younger patients with more localised disease.

REVIEW ARTICLE. THE MOLECULAR PATHOLOGY OF SMALL ROUND-CELL TUMOURS—RELEVANCE TO DIAGNOSIS, PROGNOSIS, AND CLASSIFICATION

Substantial improvements have been made in the treatment and survival of children with SRCT, resulting in an increased emphasis on precise histological diagnosis. Although diagnostic procedures such as electron microscopy and immunocytochemistry contribute in poorly differentiated cases, an accurate diagnosis can remain elusive in a proportion of SRCTs. The cytogenetic and molecular genetic abnormalities characteristic of the different SRCTs can now be consistently and rapidly identified from minimal quantities of tumour material, using the techniques of FISH and PCR. This, coupled with the identification of novel phenotypic characteristics, has had a major impact on SRCT diagnosis. The aim of a tumour classification is to identify disease entities which are biologically distinct and whose recognition is of clinical value. The recent advances described above demonstrate that the SRCTs are genotypically and phenotypically distinct tumour types and that the genetic abnormalities represent key alterations that influence both the morphology and the clinical behaviour of the tumour. This suggests that these advanced phenotypic and genotypic analyses should form an integral and complementary part of the laboratory assessment and clinical management of these forms of paediatric cancer.

Cytogenetic abnormalities in 42 rhabdomyosarcoma: a United Kingdom Cancer Cytogenetics Group Study.

BACKGROUND Rhabdomyosarcomas are the most common type of pediatric soft tissue sarcoma. The cytogenetic literature on RMS is biased towards the less common alveolar subtype (ARMS), which is frequently associated with specific translocations and the PAX3/7-FKHR fusion genes. Relatively few karyotypes are reported for the embryonal subtype (ERMS). The aim of this study was to further cytogenetic knowledge of RMS subtypes. PROCEDURE Representative examples of all karyotypes from UKCCG; member laboratories were reexamined and their histopathologies reviewed through the United Kingdom Childrens Cancer Study (Group) (UKCCSG). Molecular evidence for the PAX3/7-FKHR fusion genes was available for five ERMS and seven ARMS cases and compiled with the karyotypes. RESULTS Clonal chro mosome aberrations were characterized for 25 ERMS and 17 ARMS cases. Thirty-six percent of the ERMS cases involved translocation breakpoints in the 1p11-q11 region. Ten of the seventeen cases of ARMS showed cytogenetic evidence for the t(2;13)(q35;q14), consistent with molecular data available from four of these. Two further ARMS cases revealed a PAX3-FKHR and a variant PAX7-FKHR fusion gene product that were not detected cytogenetically. CONCLUSIONS Many of the karyotypes from both subtypes were complex. The frequent involvement of the 1p11-1q11 region and gain of chromosomes 2, 8, 12, and 13 in ERMS may be functionally significant. There was no evidence for involvement of the PAX3/7-FKHR genes in ERMS, and cryptic involvement was found in some ARMS. There were no consistent chromosomal rearrangements associated with apparently translocation negative ARMS cases.

Novel formation and amplification of the PAX7-FKHR fusion gene in a case of alveolar rhabdomyosarcoma.

Alveolar rhabdomyosarcomas frequently exhibit specific translocations, resulting in the fusion of the FKHR gene at 13q14 with either the PAX3 or PAX7 gene at 2q35 and Ip36, respectively. Comparative genomic hybridization revealed amplification at 13q14 and Ip36, suggesting amplification of the PAX7‐FKHR fusion gene in two cases of alveolar rhabdomyosarcoma. A PAX7‐FKHR fusion transcript was demonstrated in both cases by reverse transcription‐polymerase chain reaction followed by sequence analysis. In one case, amplification of the PAX7 gene and 3′‐ and 5′‐FKHR gene sequences was demonstrated by using interphase fluorescence in situ hybridization on tumor imprints. The colocalization, variable copy number, and distribution of signals from the three cosmids was consistent with amplification of these sequences on double minutes, which were present cytogenetically. Chromatin release studies suggested that the amplified sequences correlated with amplification of the PAX7‐FKHR fusion gene which resulted from the insertion of PAX7 sequences into the first intron of the FKHR gene, in keeping with the absence of cytogenetic evidence for derivative chromosomes. Genes Chromosom Cancer 17:7–13 (1996).

Interphase fluorescence in situ hybridization detection of t(2;13)(q35;q14) in alveolar rhabdomyosarcoma - A diagnostic tool in minimally invasive biopsies

The identification of t(2;13)(q35;q14) is a useful aid in the accurate diagnosis of rhabdomyosarcoma, distinguishing it from other small round cell tumours and supporting the distinction between alveolar and embryonal forms. Cytogenetic analysis is difficult and with the increased use of minimally invasive biopsy methods and primary chemotherapy, adequate tumour material is not always available. To overcome these difficulties, two‐colour interphase fluorescence in situ hybridization (FISH) to detect t(2;13)(q35;q14) was developed and its utility in assessing minimally invasive biopsies was investigated. Two cosmid clones which mapped proximal or distal to the breakpoint region 13q14 and one yeast artificial chromosome clone that mapped distal to the 2q35 breakpoint were identified. In interphase cells containing t(2;13)(q35;q14), the configuration of cosmid and yeast artificial chromosome signals demonstrated the presence of the translocation. Five cases of rhabdomyosarcoma were analysed by interphase FISH. The t(2;13)(q35;q14) was detected in all four alveolar tumours and was confirmed by cytogenetics in two cases, but was absent in one embryonal tumour. This sensitive detection method is applicable to minimal amounts of fresh or frozen tumour.

Primitive neuroectodermal tumor of the kidney confirmed by fluorescence in situ hybridization.

Peripheral primitive neuroectodermal tumors (PNETs) are rare lesions that form part of the Ewing family of tumors, which includes osseous and extraosseous Ewings sarcoma and Askins tumor of the thorax. All are characterized by translocations involving the EWS gene at 22q12, usually the translocation t(11;22)(q24;12). PNETs usually occur in soft tissues but occasionally arise within a visceral organ. We describe a PNET of the kidney that showed characteristic microscopic and immunohistochemical appearances of a small, round, dark blue cell tumor with focal rosette formation and strong membrane positivity for the MIC2 gene product. Interphase fluorescence in situ hybridization on touch imprints prepared from frozen tissue using cosmid probes flanking the EWS gene at 22q12 and the FLI1 gene at 11q24 indicated the presence of t(11; = +22)(q24; = +q12), confirming the diagnosis of PNET. This is the first reported PNET of the kidney supported by cytogenetic analysis. We also review the literature on this fascinating tumor in this unusual location.

Chromosomal imbalances in pleomorphic rhabdomyosarcomas and identification of the alveolar rhabdomyosarcoma-associated PAX3-FOXO1A fusion gene in one case

Rhabdomyosarcomas (RMS) are soft tissue sarcomas resembling developing skeletal muscle, and pleomorphic rhabdomyosarcomas (PRMS) are a rare nonpediatric entity. Little molecular cytogenetic information exists for PRMS, and their relationship to other subtypes of rhabdomyosarcoma and other sarcomas is unclear. Chromosomal imbalances were determined in seven well-characterized cases of PRMS using comparative genomic hybridization. The smallest overlapping regions of gain were 1p22 approximately p33 (71%), 7p (43%), 18/18q (43%), and 20/20p (43%), and the regions of loss were 10q23 (71%), 15q21 approximately q22 (57%), 3p, 5q32 approximately qter, and 13 (all 43%). Four of the seven cases had amplicons involving the regions 1p21 approximately p31, 1q21 approximately q25, 3p12, 3q26 approximately qtel, 4q28 approximately q31, 8q21 approximately q23/8q, and 22q. These regions are distinct from those frequently associated with the alveolar subtype, whereas the embryonal subtype without anaplasia is rarely associated with amplification events other than gain/amplification of 8q material. The regions of imbalance appeared more similar to those reported for malignant fibrous histiocytomas (MFH) and osteosarcomas, consistent with the suggestion that PRMS can be considered part of the spectrum of MFH. In addition, one of the cases classified as PRMS showed evidence for the presence of a PAX3-FOXO1A fusion gene, which is characteristic of the alveolar subtype of RMS.

der(16)t(1;16)(q21;q13) as a secondary change in Alveolar Rhabdomyosarcoma: A case report and review of the literature

Alveolar rhabdomyosarcoma is an aggressive childhood tumor that exhibits muscle cell differentiation. Cytogenetically, it is characterized by t(2;13)(q35;q14); no consistent secondary abnormalities have been reported. Cytogenetic analysis of bone marrow in a case of alveolar rhabdomyosarcoma revealed t(2;13)(q35;q14) and der(16)t(1;16)(q21;q13). The present case and a review of the literature suggest that up to 11% of these tumors possess der(16)t(1;16)(q21;q13). This is similar to the incidence observed in the Ewing family of tumors, where unbalanced der(16)t(1;16) translocations, resulting in partial trisomy of 1q, are regarded as a consistent secondary cytogenetic change.

Two unbalanced translocations, t(12;22)(p13;q11) and t(12;?)(p13;?), in an aggressive chronic B-cell leukemia: TEL gene analysis using FISH.

The translocation t(12;22)(p13;q11) has been consistently described in myeloid malignancies and shown to result from a fusion between the TEL and MN1 genes. Previously described deletions of 12p in acute lymphoblastic leukemias have been recently shown to harbor undetected translocations involving the TEL gene at 12p13. We document a case of an aggressive chronic B-cell leukemia whose cells had trisomy 12 and two unbalanced translocations involving 12p13, including a t(12;22)(p13;q11) as shown by conventional cytogenetics and fluorescence in situ hybridization (FISH). The 12p13 breakpoint of the t(12;22)(p13;q11) was telomeric to the TEL gene, and the second unbalanced translocation with breakpoint 12p13 resulted in the deletion of TEL. This case demonstrates that TEL gene deletions may be relevant in cases of mature B-lymphoproliferative diseases.