Abstract 1422: HighFLT3mRNA expression withoutFLT3-ITD in infants with acute myeloid leukemia

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Introduction: When compared to older patients, infants with acute leukemia exhibit high frequency of MLL gene rearrangement (MLL-R), and are known to have higher vulnerability to intensive cytotoxic therapy, such as hematopoietic stem cell transplantation (HSCT). In contrast to acute lymphoblastic leukemia (ALL) in infants, there have been a few reports on acute myeloid leukemia (AML) in infants including our group (A. Shimada et al, ASH 2011). We and other group reported that MLL-R had the clinical impact in infant ALL, however, not in infant AML. Infant ALL with MLL-R expressed high FLT3 mRNA, on the other hand, the importance of FLT3 mRNA remains to be obscure in infant AML. Patients: Forty four infants with AML, aged less than 1 year at diagnosis, registered in JPLSG AML-05 from 2006-2010. Patients with Down syndrome were excluded. The most frequent FAB classification type was M7 (18/44, 40.9%), followed by M5 (15/44, 34.1%), and M4 (4/44, 9.0%). Total 16 of 44 (36.4%) infant AML patients had MLL-R, 9 patients were detected by G-banding method, and other 7 patients were by FISH analysis or RT-PCR. There was not t(8;21), t(15;17) except for one inv(16) patient. Methods: FLT3 mRNA expression and internal tandem duplication (ITD) were analyzed in the first diagnostic bone marrow samples by RQ-PCR and PCR. Results: No patients had FLT3-ITD, however, higher FLT3 mRNA expression was found in MLL-R patients (n=16) (median 623,150 copies/μgRNA) compared with MLL-wild type (WT) (n=28) (median 25,105) (p<0.005). This phenomenon was also observed in 12-23 months AML patients. Discussion: High FLT3 mRNA expression was reported in infant ALL with MLL-R and it can be a molecular target for FLT3 inhibitor. On the other hand, there was no report in infant AML. Our previous data suggested that SCT had the limited efficacy for infant AML, FLT3 inhibitor might be considered to be used for infant AML with MLL-R in future. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1422. doi:1538-7445.AM2012-1422