Short Communication Detection of HEY1-NCOA2 fusion by fluorescence in-situ hybridization in formalin-fixed paraffin-embedded tissues as a possible diagnostic tool for mesenchymal chondrosarcoma Robert Nakayama, 1 Yasuhiro Miura, 2 Jiro Ogino, 2 Michiro Susa, 1 Itsuo Watanabe, 1 Keisuke Horiuchi, 1 Ukei Anazawa, 3 Yoshiaki Toyama, 1 Hideo Morioka, 1 Makio Mukai 4 and Tadashi Hasegawa 2 1 Department of Orthopaedic Surgery, Keio University School of Medicine, Tokyo, Japan, 2 Department of Surgical Pathology, Sapporo Medical University School of Medicine, Sapporo, Japan, 3 Department of Orthopaedic Surgery, Tokyo Dental College Ichikawa General Hospital, Ichikawa, Japan, and 4 Division of Diagnostic Pathology, Keio University School of Medicine, Tokyo, Japan. Mesenchymal chondrosarcoma (MC) is an extremely rare subtype of chondrosarcoma. A tumor specific fusion gene, HEY1-NCOA2 fusion, was recently identified in this tumor. The finding raises the possibility that the diagnosis of MC can be improved by examining the fusion gene. In the present study, we aimed to evaluate the efficacy of fluores- cence in situ hybridization (FISH) in detecting HEY1-NCOA2 fusion for the diagnosis of MC. Specimens from 10 patients diagnosed with MC were used for the study. Dual-color FISH was performed using two different probes that specifically hybridize to HEY1 and NCOA2, respectively. Fusion signals were identified in all but two specimens, in which no signal was detected, presumably because of inadequate sample preparation. In accordance with results of a previous study, FISH analysis was highly sensitive in detecting HEY1- NCOA2 fusion in adequately prepared MC samples. The current study adds further support for the use of HEY1- NCOA2 fusion as a valid diagnostic marker for MC. Key words: fluorescence in situ hybridization, fusion gene, mesenchymal chondrosarcoma Mesenchymal chondrosarcoma (MC) is an extremely rare subtype of chondrosarcoma, comprising less than 10% of all chondrosarcoma cases (7.2% in the Bone and Soft Tissue Tumor Registry at Keio University Hospital, Tokyo, Japan). 1–3 It commonly affects young adults 1,4,5 and arises not only in the bone, 6–8 but also at a wide variety of sites including the soft tissue, central nervous system and meninges. 9–11 Histo- logically, it is characterized by a bimorphic pattern composed of highly undifferentiated small round cells (Ewing sarcoma- like area) and islands of well-differentiated hyaline cartilage (chondroid area) (Fig. 1). 1,8 Histological diagnosis of MC can be challenging since the proportion of these two compo- nents vary widely among cases and, therefore, chondroid matrix formation is often inconspicuous under microscopic analysis. 12–16 Recently, a chimera gene, HEY1-NCOA2 fusion, was identified by a genome-wide bioinformatic screen in MC. 17 HEY1 and NCOA2 are located on 8q21and 8q13, respectively, spanning approximately 10 Mb from one another. The chimeric transcript, HEY1-NCOA2, is derived from a chromosomal deletion between exon 4 of HEY1 and exon 13 of NCOA2. The resulting fusion gene gives rise to a chimeric protein bearing the DNA-binding domain of HEY1 and the C-terminal transcriptional activation domains of NCOA2. 17 This finding is expected to improve pathological diagnosis and to facilitate further investigation of the patho- genesis of this tumor. In this study, 10 paraffin-embedded samples were analyzed to evaluate the efficacy of fluores- cence in situ hybridization (FISH) in detecting HEY1-NCOA2 fusion for the diagnosis of MC. MATERIALS AND METHODS Case selection A search of our database for the period from 1995 to 2012 yielded 10 cases which had been diagnosed with MC (Table 1). Each tumor specimen was histologically reviewed Correspondence: Tadashi Hasegawa, Md, PhD, Department of Sur- gical Pathology, Sapporo Medical University School of Medicine, South 1, West 16, Chuo-ku, Sapporo 060-8543, Japan. Email: hasetada@sapmed.ac.jp Received 3 September 2012. Accepted for publication 23 November 2012. © 2012 The Authors Pathology International © 2012 Japanese Society of Pathology and Wiley Publishing Asia Pty Ltd Pathology International 2012; 62: 823–826 doi:10.1111/pin.12022