An Overall Characterization of Pediatric Acute Lymphoblastic Leukemia with CRLF2 Overexpression Mio Yano, 1 Toshihiko Imamura, 1 * Daisuke Asai, 1,2 Akiko Moriya-Saito, 3 So-ichi Suenobu, 4 Daiichiro Hasegawa, 5 Takao Deguchi, 6 Yoshiko Hashii, 7 Hirohide Kawasaki, 8 Hiroki Hori, 6 Yoshiyuki Kosaka, 5 Koji Kato, 9 Keizo Horibe, 3 Keiko Yumura-Yagi, 10 Junichi Hara, 11 Kenji Matsumoto, 12 Nobutaka Kiyokawa, 13 Megumi Oda, 14 and Atsushi Sato, 15 for the Japan Association of Childhood Leukemia Study (JACLS) 1 Department of Pediatrics,Kyoto Prefectural University of Medicine,Graduate School of Medical Science,Kyoto, Japan 2 Division of Pediatrics, Fukuchiyama City Hospital, Fukuchiyama, Japan 3 Clinical Research Center, National Hospital Organization Nagoya Medical Center, Nagoya, Japan 4 Division of General Pediatrics and Emergency Medicine, Department of Pediatrics,Oita University,Oita,Japan 5 Department of Hematology/Oncology, Hyogo Prefectural Children’s Hospital,Kobe, Japan 6 Department of Pediatrics, Mie University,Tsu, Japan 7 Department of Pediatrics,Osaka University,Osaka, Japan 8 Department of Pediatrics,Kansai Medical University, Hirakata,Japan 9 Department of Pediatrics, Japanese Red Cross Nagoya Daiichi Hospital, Nagoya, Japan 10 Department of Pediatrics,Osaka General Medical Center,Osaka, Japan 11 Department of Pediatrics,Osaka City General Hospital,Osaka,Japan 12 Department of Allergy and Immunology, National Center for Child Health and Development,Tokyo, Japan 13 Department of Pediatric Hematology and Oncology Research, National Center for Child Health and Development,Tokyo, Japan 14 Department of Pediatrics,Okayama University,Okayama, Japan 15 Department of Pediatric Hematology/Oncology, Miyagi Children’s Hospital, Sendai, Japan For an overall characterization of pediatric B-cell precursor acute lymphoblastic leukemia (BCPALL) with CRLF2 overex- pression (OE), we conducted genetic analysis of CRLF2 in 167 pediatric BCPALL patients. CRLF2 OE was detected in 30 (18%) of 167 patients, the P2RY8-CRLF2 fusion was identified in only 3 (1.8%) of 167 patients, all of which demonstrated CRLF2 OE. Moreover, CRLF2 gain was identified in 18 (11%) of 167 patients. Messenger RNA sequencing revealed a novel fusion transcript, CSF2RA-CRLF2, in a case with CRLF2 OE, suggesting that this fusion is associated with CRLF2 OE. In sur- vival analysis, no significant differences in 5-year event-free survival (EFS) and overall survival were observed between patients with and without CRLF2 OE (70.7 vs. 75.4%, log rank P 5 0.68 and 96.4 vs. 82.1%, log rank P 5 0.11, respectively). However, a significant difference in 5-year EFS between CRLF2 OE patients with and without IKZF1 deletion was observed (44.4 vs. 83.1%, log rank P 5 0.02). In multivariate analysis, only IKZF1 deletion was a significant predictor of inferior OS (hazard ratio: 2.427, P 5 0.04).These findings suggest that CRLF2 OE is not an independent prognostic factor in pediatric BCPALL. V C 2014 Wiley Periodicals, Inc. INTRODUCTION Approximately 20% of pediatric acute lympho- blastic leukemia (ALL) patients still have a poor outcome, despite progress in intensified therapies and the development of detailed risk classifications (Pui et al., 2011). To improve the prognosis of high risk pediatric ALL, the identification of novel prognostic factors and therapeutic targets are required. As patients who lack recurrent cytoge- netic abnormalities are known to be at higher risk of poor outcome, IKZF1 deletion (Mullighan et al., 2009b; Kuiper et al., 2010; Waanders et al., 2011), CRLF2 overexpression (OE), and BCR-ABL1-like gene expression profile (GEP; Den Boer et al., 2009; Harvey et al., 2010b; Roberts et al., 2012) have recently been intensively studied as potential prognostic factors. Previous studies have described the prognostic significance of CRLF2 OE and CRLF2 rearrange- ments, including P2RY8-CRLF2 and IgH-CRLF2 Supported by: Grants for Clinical Cancer Research and Research on Measures for Intractable Diseases from the Japanese Ministry of Health, Labor, and Welfare; grants-in-aid for scientific research from the Japanese Ministry of Education, Culture, Sports, Science, and Technology. *Correspondence to: Toshihiko Imamura, Department of Pedia- trics, Kyoto Prefectural University of Medicine, Kajii-cho, Hirokoji, Kamigyo-ku, Kyoto 602–8566, Japan. E-mail: imamura@koto.kpu-m.ac.jp Received 18 May 2014; Accepted 24 May 2014 DOI 10.1002/gcc.22190 Published online 17 June 2014 in Wiley Online Library (wileyonlinelibrary.com). V V C 2014 Wiley Periodicals, Inc. GENES, CHROMOSOMES & CANCER 53:815–823 (2014)