Cancer Genetics and Cytogenetics 144 (2003) 125–133 Cytogenetic and molecular findings related to rhabdomyosarcoma. An analysis of seven cases Rosario Gil-Benso, Concha Lo ´pez-Gine ´s, Carmen Carda, Jose ´ Antonio Lo ´pez-Guerrero, Jaime Ferrer, Antonio Pellı ´n-Pe ´rez, Antonio Llombart–Bosch Department of Pathology, Medical School, University of Valencia, Avda. Blasco Iba ´n ˜ez 17, Valencia 46010, Spain Received 27 August 2002; received in revised form 27 December 2002; accepted 8 January 2003 Abstract Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in childhood. Histologically, it is subdivided histologically into two main subtypes: alveolar (ARMS) and embryonal (ERMS). ARMS is characterized by t(2;13)(q35;q14) or its variant t(1;13)(p36;q14), which fuse PAX3 and PAX7, respectively, with FKHR to produce chimeric genes. ERMS is frequently associated with loss of heterozygosity of 11p15.5. We investigated seven RMS (three ARMS and four ERMS) by means of cytogenetic, fluorescence in situ hybridization, and molecular analyses, including the study of the main genes implicated in the G1- to S-phase cell cycle transition, and correlated these studies with pathologic findings and clinical outcome. All tumors showed clonal, numerical, and structural chromosomal abnormalities. Two ARMS had the t(2;13)(q35;q14) and the third a PAX7/FKHR fusion, a cryptic t(1;13)(p36;q14), undetected by cytogenetic techniques, but revealed by reverse transcriptase polymerase chain reaction. One ERMS showed a der(11)t(3;11)(p21;p15) as a sole structural anomaly. Gene amplification was seen in four tumors, as double minutes or in the form of homogeneously staining regions. Overexpression of MYCN oncogene was found in two ARMS; N-myc DNA probe detected oncogene amplification located on the double minutes of these cases. Analysis of the regulatory genes responsible for G1- to S-phase transition showed a homozygous deletion of the 9p21 locus genes in a spindle-cell ERMS.  2003 Elsevier Inc. All rights reserved. 1. Introduction Rhabdomyosarcoma (RMS) is the most common soft- tissue sarcoma affecting individuals under the age of 25 [1]; it accounts for ~10% of all pediatric solid tumors [1,2]. These tumors originate from the undifferentiated mesenchymal cells resembling developing striated muscle. RMS is subdi- vided into embryonal (ERMS), alveolar (ARMS), and pleo- morphic subtypes using histologic criteria [3]. ERMS mainly develops in younger children. It appears in the head and neck region, genitourinary tract, and the retroperitoneum. It is associated with a favorable prognosis. ARMS develops mainly in adolescents and young adults, often occurring in the extremities and trunk, and is considered to be clinically more aggressive. Diagnosis of RMS may be complicated because of the subtle histologic criteria for distinguishing RMS subtypes, the presence of more than one histologic * Corresponding author. Tel.: +34-963864146; fax: +34-963864173. E-mail address: Rosario.Gil-Benso@uv.es (R. Gil-Benso). 0165-4608/03/$ – see front matter  2003 Elsevier Inc. All rights reserved. doi: 10.1016/S0165-4608(03)00026-8 pattern, and the tendency for RMS and other pediatric solid tumors for having poorly differentiated cells. Cytogenetic studies have demonstrated that about 70% of the ARMS are characterized by t(2;13)(q35;q14) or the variant t(1;13)(p36;q14). Both translocations result in chimeric tran- scripts encoding a fusion protein consisting of the intact PAX3 or PAX7 DNA-binding domain and the distal half of the fork head domain of the FKHR gene [4–6]. Cytogenetically, ERMS is usually hyperdiploid with a gain of chromosomes 2, 7, 8, 11, 12, and 13, with a particularly high level of chromosome 8 material, although no consistent structural chromosomal changes have been found. ERMS is fre- quently characterized by loss of heterozygosity (LOH) of 11p15.5 and these LOH studies define the putative tumor suppressor gene distal to D11S988 locus [7,8]. Furthermore, several genes on 11p15.5 are subject to imprinting, which complicates the LOH studies [9]; ERMS shows a preferential retention of the paternal chromosome 11, suggesting a role of epigenetic modifications in the process of tumor develop- ment [9,10].