Abstract: The t(8;21) is one of the most frequent chromosomal translocation in acute myeloid leukemia (AML). The t(8;21) AML is commonly associated with a favorable prognosis in regard to overall survival (OS) as well as high complete remission (CR) rate. However, approximately 35–45% of patients in first CR will relapse within 5 years. In t(8;21) AML, a worse outcome has been reported in patients with a high presenting white blood cell count, expression of CD56, and activating mutation of c-Kit (D816V). The clinical outcome of t(8;21) AML in first relapse have not been clarified. Further, factors predicting the outcome of patients in first relapse have not been defined. In this study, we evaluated the clinical features, the prognostic significance of c-Kit (D816V) mutation and karyotype instability in 14 relapsed patients among 32 de novo t(8;21) AML patients treated in our institution during the period 1987 to 2006. These 32 patients’ ages ranged from 15 to 73 years (median, 46 years) and they were classified as RAEB-T (n=2), M1 (n=2) and M2 (n=28) according to the FAB classification. Another additional cytogenetic aberrations at diagnosis were loss of Y (n=5), del(9q) (n=3), del(7q) (n=1), and trisomy 4 and 6 (n=1). Of the 32 patients, 14 (44%) were treated with BHAC-DMP (behenoylcytosine arabinoside, daunorubicin, 6-mercaptopurine, and prednisolone) induction therapy and 18 (56%) were treated with induction therapy consisted of an idarubicin or daunorubicin in combination with cytarabine (200mg/m2 for 7 days). For post remission therapy, 26 (82%) were received sequential multiagent chemotherapy and 6 (18%) were received high dose cytarabine alone. All patients achieved first CR (100%), median OS and disease-free survival (DFS) was 5.1 years and 2.4 years, respectively. 14 (44%) had a relapsed and the median duration from initial diagnosis to relapse amounted to 10.5 months (range, 3.8 months to 2.4 years). Among the 14 relapsed patients treated with salvage therapy, 9 (64%) of patients achieved second CR and median OS and DFS after first relapse was 2.0 years and 1.0 year. 4 patients (12%) with c-Kit (D816V) mutation at first diagnosis relapsed within 12 months with the same mutation and died within 2.2 years. Karyotype examination at first relapse were performed in 12 patients and additional karyotypic abnormalities were found in 6 patients. Three or more complex aberrations involving del(5q), del(6q), del(7q) or del(9q) were found in all of 6 patients. Among 6 patients showing karyotypic evolution (KE), 5 achieved second CR and relapsed again shortly. Two patients with KE had c-Kit D816 mutation at diagnosis, however, c-Kit mutations of exon 17 and 8 were not detected in 4 patients with KE at diagnosis and during the course of disease. In conclusion, karyotypic instability is common in t(8;21) AML at relapse and is not associated with c-Kit mutation. Karyotypic instability may contribute to the development of refractoriness of AML to chemotherapy.

Abstract: In hematologic malignancies, deletion of 3p25-26 is a rare but recurrent cytogenetic aberration, indicating the presence of tumor suppressor gene (TSG) on this choromosome arm. We revealed a t(3;5)(p25;q35) that was identified by conventional cytogenetics results in a novel fusion of KIAA0379 on 3p25 to NUP98 on 11p15 in a patient with refractory MDS/AML by the molecular analysis. Fluorescence in situ hybridization (FISH) analysis using whole chromosomal painting and telomeric probes unclosed a criptic three-way translocation t(3;5;11)(p25;q35;p15). FISH restriction using BAC contig revealed that the 3p25 breakpoint is involved in KIAA0379 which locates between BAC 792N12 and 259O19. Split signals of BAC 265K23 for 5q35 and 348A20 for 11p15 showed that NSD1 on 5q35 and NUP98 on 11p15 are the responsible genes of this translocation. As the results of this translocation, expression of three chimeric transcripts were identified by RT-PCR. In KIAA0379-NUP98, exon 18 of KIAA0379 was fused in-flame with exon 13 of NUP98. In NUP98-NSD1, exon 12 of NUP98 was fused in-flame with exon 7 of NSD1. NSD1-KIAA0379 resulted in out-flame fusion. To investigate the expression of KIAA0379 in leukemic cells, RT-PCR for full-length KIAA0379 transcript was performed on bone marrow cells from the patient and a healthy volunteer, and leukemic cell line K562, HL-60 and KG-1a cells. Full-lengh PCR product with expected size was found in all samples, however, short variant transcript was amplified significantly from KG-1a and HL-60 cells. Subsequent sequence analysis of the short PCR product from KG-1a cells revealed a direct fusion of a part of exon 10 to a part of exon 28 without any hidden splicing sites. Southern blot analysis using a cloned KIAA0379 cDNA fragment suggested an internal deletion of KIAA0379 in KG-1a cells. KIAA0379 locates at 3p25.1 about 5.5Mb centromeric to VHL and is predicted to have 28 ankyrin repeat motifs by computational analysis. It is thought to be involved in protein to protein interaction whereas its precise funtion remains unclear. Immunostaining for KIAA0379 protein in NIH3T3 cells transfected with the wild KIAA0379 and the short variant KIAA0379 revealed that the wild KIAA0379 protein localized in cytoplasm and nuclear membrane, on the other hand, the truncated KIAA0379 protein localized exclusively on nuclear membrane. KIAA0379-NUP98 fusion protein is expected to localize on nuclear membrane by sub-localization signal of C-terminal of NUP98. Therefore, dysfunction of KIAA0379 protein might lead to leukemogenesis and KIAA0379 may be potential candidate for a novel TSG. In addition, it has been reported that t(5;11)(q35;p15.5) results in NUP98-NSD1 fusion in childhood AML. To our knowledge, this is the first report in adult case.

Abstract: Background and Aim: Therapy-related chronic myeloid leukemia (TR-CML), which is defined as CML that developed after exposure to cytotoxic chemotherapy and/or radiotherapy, rarely exists in clinical practice, although its incidence rates are relatively lower than those of acute myeloid leukemia or myelodysplastic syndromes, accounting for 1.2-30.4% of secondary leukemias. The clinical behavior of TR-CML, including patient outcome, is reportedly not different from that of de novo CML before the era of imatinib treatment. While the recent advancement of CML treatment by the introduction of tyrosine kinase inhibitors (TKIs) has dramatically improved treatment outcomes in patients with CML, little is known about the treatment response and outcomes in patients with TR-CML treated with TKI. In this regard, we investigated the clinical entity of TR-CML in the era of TKIs, including treatment response to TKI and prognosis, in patients enrolled to the CML Cooperative Study Group. Patients and Methods: We retrospectively reviewed the data of patients enrolled in the CML Cooperative Study to identify patients diagnosed with TR-CML. This study included patients aged 〉 15 years who were diagnosed with CML in the chronic phase between April 2001 and January 2016, and treated with any TKIs as initial therapy and followed up for at least 3 months. The study was approved by the research ethics board of each institution and conducted in accordance with the Declaration of Helsinki. A major molecular response (MMR) was defined as ≤0.1% on the International Scale (IS) or 100 copies of the BCR-ABL1 transcript/μg RNA in a transcription-mediated amplification and hybridization protection assay. A deep molecular response (DMR) was defined ≤0.0032% in the IS. Event-free survival (EFS) was defined as the period from the date of initial treatment with TKI to the date of onset of the first adverse event (loss of treatment efficacy, progression to the accelerated or blastic phase, or any cause of death) or the last follow-up. Statistical analyses were performed by using EZR. Results and Discussion: We identified 308 patients with newly diagnosed CML in the chronic phase, including 11 (3.6%) with TR-CML and 297 with de novo CML. Regarding the primary cancer, 2 of the 11 patients had breast cancer and the remaining 9 had prostate cancer, pharyngeal cancer, mesothelioma, lung cancer, colon cancer, ureter cancer, acute leukemia, gastric cancer, or bladder cancer, respectively. Eight cases were treated with chemotherapy, 2 were treated with radiotherapy, and the remaining case was treated with both chemotherapy and radiotherapy. The results of a cytogenetic analysis by G-banding were exclusive t(9;22)(q34;q11) in all the patients. The median time to diagnosis of CML from the initiation of chemotherapy and/or radiotherapy was 7 years (range, 1.2-33 years). No significant differences in patient age, sex, white blood cell count, hemoglobin level, platelet count, or European Treatment and Outcome Study risk were observed between the TR-CML and de novo CML groups. Among the patients whose cytogenetic and/or molecular responses were assessable, all had excellent treatment response to TKI. Seven patients unexpectedly reached MMR within 6 months after TKI initiation. Finally, 8 patients attained DMR or undetectable leukemia in the bone marrow and the remaining 3 attained MMR. The 5-year EFS of the patients in the de novo CML group was 90%. None of the patients in the TR-CML group experienced any adverse event. In conclusion, in the present study, we revealed that patients with TR-CML could attain a good clinical course with TKI therapy. Detailed investigations of TR-CML may provide new insights into the CML biology. Disclosures Iriyama: Novartis: Honoraria, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Speakers Bureau. Takaku:Bristol: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau. Nakazato:Mundipharma KK: Research Funding. Fujita:Chugai Pharmaceutical Co.,LTD: Honoraria. Tokuhira:Bristol Myers Squibb Co., Ltd: Honoraria; Pfizer Co., Ltd: Honoraria; Eizai Co., Ltd: Honoraria. Kawaguchi:Novartis: Honoraria.

Abstract: We previously reported that TEL-FGFR3 in a patient with peripheral T-cell lymphoma and AML conferred IL-3 independency to Ba/F3 cells and activates MAPKs, p38, PI3K, Stat3 and Stat5 through its constitutive tyrosine kinase (TK) activity in TEL-FGFR3 transfected Ba/F3 cells (TF-V5). Recent report suggests that FGFR3 activates Stat5 through recruitment of Pyk2 (proline-rich tyrosine kinase 2) to its juxta-membrane (JM) domain. To gain insight into the roles of Pyk2-Stat5-Bcl-xL axis in TEL-FGFR3 associate tumorigenesis, we performed a functional analysis of a deletion mutant of TEL-FGFR3 which lacks the JM domain. Stable polyclonal transfectants of Ba/F3 cells expressing the deletion mutant of TEL-FGFR3(ΔJM-V5) grew in absence of IL-3 without spontaneous apoptosis by constitutive TK activity. ΔJM TEL-FGFR3 did not recruit Pyk2 and induced little phosphorylation of Stat3 and Stat5 compared to those of TF-V5, while it induced constitutive phosphorylation of MAPKs and PLCγ. In ΔJM-V5, expressions of Bcl-xL and Bcl-2 were abrogated to the level of Mock without IL-3. To elucidate a mechanism of IL-3 independent cell growth of ΔJM-V5 which does not express Bcl-xL and Bcl-2, we examined expression of pro-apoptotic Bcl-2 families and revealed that Bax was not expressed in ΔJM-V5. In TF-V5, Bax was constitutively expressed and FGFR3 TK inhibitor SU5402 inhibited Bax expression after 24hr. These results indicate that there might be a pathway from JM domain to regulate Bax expression. To examine the role of Bcl-xL and Bcl-2 in DNA damage-induced apoptosis, TF-V5 and ΔJM-V5 were X-irradiated with 5, 15, 30 or 50Gy respectively. TF-V5 had reduced susceptibility to apoptosis following X-irradiation when compared with Mock transfected cells without IL-3. In TF-V5 the presence of IL-3 did not affect susceptibility to X-ray-induced apoptosis at any dose levels. In contrast, when ΔJM was treated with IL-3, significant reduced susceptibility to X-ray irradiation at more than 15Gy was observed (apoptotic fraction following 30Gy irradiation after 24hr: 40% without IL-3; 20% with IL-3). In ΔJM cells, IL-3 induced over-expression of Bcl-xL and Bcl-2 and cell cycle arrested at G1 was observed following more than 15Gy X-irradiation. Taken together, it is supposed that Bcl-xL and Bcl-2 play an anti-apoptotic role only when Bax is induced by activated p53 in ΔJM-V5. Further, to investigate leukemogenesis of ΔJM-V5 in vivo, ΔJM-V5 cells were injected intravenously into BALB/c mice. As a result, although all 10 mice intravenously injected ΔJM-V5 developed a disease resembling leukemia with enlargement of spleen and died within 30 days after injection, they exhibited a significantly prolonged disease latency (median survival=23.6 days) compared to all 10 mice intravenously injected TF-V5 died of a similar disease (median survival=18.0 days). Our results indicate that ΔJM does not activate Stat3 and Stat5 without Pyk2 recruitment and not express Bcl-xL, Bcl-2 and Bax. Conclusion: Both Bcl-xL and Bcl-2 are dispensable for a TEL-FGFR3 transforming property especially in ΔJM-V5 which does not express Bax. However, Bcl-xL and Bcl-2 might be necessary for full oncogenic property of ΔJM TEL-FGFR3.

Abstract: Background and Aim: Treatment with a tyrosine kinase inhibitor (TKI) is the standard of care for patients with chronic myeloid leukemia (CML). Based on the results of the ENESTnd and DASISION studies, the European LeukemiaNet 2013 guidelines now recommend the use of TKIs, imatinib (400 mg once daily), nilotinib (300 mg twice daily), and dasatinib (100 mg once daily) as first-line treatment for patients with CML in the chronic phase (CML-CP). Compared to imatinib, the new generation TKIs, nilotinib and dasatinib, were found to have deeper and faster treatment response rates with acceptable toxicities. However, a direct comparison between nilotinib and dasatinib has never been reported previously. Our study aims to compare the outcomes and molecular responses achieved following the first-line use of these two agents in patients with CML-CP. Patients and Methods: The database of the CML Cooperative Study Group, which includes patients who were initially diagnosed with CML after the introduction of imatinib (April 2001), was reviewed, and patients who were given nilotinib or dasatinib as first-line therapy were identified. The event-free survival (EFS, defined as the loss of treatment efficacy, disease progression, or any cause of death), and rates of cumulative major molecular response (MMR), and deep molecular response (DMR, defined as the depth of MR 4.5) were compared between the nilotinib and dasatinib groups. Further, the predictive ability of the Sokal, Hasford, and European Treatment and Outcome Study (EUTOS) scoring systems for the achievement of molecular responses was also evaluated. For the analysis of molecular responses, patients who switched from their initial treatment agent to another TKI before achievement of MMR or DMR were considered to have no MMR or DMR. Results and Discussion: Out of 361 patients with CML-CP enrolled in our database, 58 and 63 were treated with conventional doses of nilotinib (300 mg twice daily) and dasatinib (100 mg once daily), respectively, as first-line therapy. Patients who had been started on a low dose TKI therapy were excluded from this analysis. The patient demographics, including age, sex, observation periods, and the Sokal, Hasford, and EUTOS scores did not show significant differences between the groups. In total, there were five events during the observation period (1 in the nilotinib group and 4 in the dasatinib group), and all events were deaths unrelated to CML, except for one in a patient in the dasatinib group who showed loss of complete cytogenetic response. The disease did not progress to the accelerated or blastic phase in any of the cases. The EFS did not differ between these two groups (p = 0.214). The MMR rates by 6, 12, 18, and 24 months were 59%, 72%, 74%, and 81%, respectively, in the nilotinib group and 52%, 73%, 81%, and 86%, respectively, in the dasatinib group. The DMR rates by 6, 12, 18, and 24 months was 7%, 17%, 24%, and 28%, respectively, in the nilotinib group and 3%, 16%, 25%, and 29%, respectively, in the dasatinib group. During the first 24 months of treatment, 4 (7%) patients in the nilotinib group and 11 (17%) in the dasatinib group had been switched to other TKIs (p = 0.0983). Among the three scoring systems, only the Hasford score could predict the achievement of DMR, and all of them failed to predict the achievement of MMR in the entire cohort. Our data suggest that both nilotinib and dasatinib have comparable efficacies, with high molecular response rates and promising outcomes. The validity of our findings should be tested in a randomized study, which is currently underway in Japan. Disclosures Takaku: Bristol-Myers Squibb: Honoraria, Speakers Bureau; Novartis Pharma K.K.: Honoraria, Speakers Bureau. Tokuhira:Mitsubishi Tanabe Pharma Corporation: Speakers Bureau; Bristol-Myers Squibb: Speakers Bureau; AYUMI Pharmaceutical Corporation: Speakers Bureau; Chugai: Speakers Bureau. Asou:Eisai Co., Ltd.: Research Funding; SRL Inc.: Consultancy; Yakult Honsha Co., Ltd.: Speakers Bureau; Kyowa Hakko Kirin Co., Ltd.: Speakers Bureau; Asahi Kasei Pharma Co., Ltd.: Research Funding; Astellas Pharma Inc.: Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding. Kizaki:Nippon Shinyaku,: Research Funding, Speakers Bureau; Celgene: Research Funding, Speakers Bureau; Bristol-Myers Squibb: Research Funding, Speakers Bureau; Novartis: Speakers Bureau. Kawaguchi:Novartis Pharma K.K.: Honoraria, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Speakers Bureau; Alexion: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau.

Abstract: Introduction: Imatinib have dramatically changed the natural history of chronic myeloid leukemia (CML) leading to significant improvement in clinical outcome and survival rates. Recently, treatment free remission (TFR) is one of the goals in CML treatment, and some prospective trials suggest that imatinib therapy may be safely discontinued in CML patients with deep and sustained molecular responses (Mahon Lancet Oncol 2010, Ross Blood 2013, Rousselot JCO 2014). The purpose of this study was to confirm TFR in Japanese CML patients and to define prognostic biomarkers of successful TFR after stopping imatinib. Methods: Japanese CML patients on imatinib treatment in confirmed deeper molecular response (DMR) for at least two year ( & gt;4 log reduction on imatinib therapy for & gt;24 months confirmed by four consecutive PCR tests) and under imatinib treatment for at least 3 years were eligible. Patients treated with other tyrosine kinase inhibitors or who received stem cell transplantations were excluded. MR4.5 was confirmed at the beginning of this study using Ipsogen BCR-ABL1 M-BCR IS-PCR kit in a central laboratory (Sysmex, Kobe, Japan). Primary endpoint was the major molecular remission (MMR) rate at 12 months after stopping imatinib. Molecular recurrence of CML was defined as loss of MMR according to A-STIM criteria (Rousselot JCO 2014). Results: From November 2013 to March 2014, 77 CML patients in chronic phase from 26 institutions were enrolled in this study. Nine were excluded (consent withdrawal n=1, not eligible n=8). Of the eligible 68 patients, 38.2% were female. Median age was 55.0 years (range, 23 to 84), and 13.2% and 16.2 % were high-risk according to EUTOS and Sokal Scores. Thirteen patients were treated with interferon prior to imatinib therapy. Median duration of imatinib treatment was 8 years (range, 3-12 years). The duration of imatinib treatment was less than 5 years in 12%, 5-8 years in 34% and & gt; 8 years in 54% of pts. Time to MMR was 11.5 months (25%-75%, 7.5-22.7 months) and time to DMR (not detected by PCR) was 30.6 months (25%-75%, 17.6-59.9 months). Among the 68 patients, 46 patients (67.6%, 95%CI: [56.5% to 78.8%]) remained without molecular recurrence the first 12 months according to A-STIM criteria, defined as loss of MMR. Moreover, 43 patients (63.2%, 95%CI: [51.8% to 74.7%] ) remained without molecular recurrence the first 12 months according to STIM criteria, defined as two consecutive loss of MR4.5 with 1 log increase. On the other hand, 22 patients who lost MMR were treated again with imatinib and all patients achieved MMR within 6 months. Time to 2nd MMR was 40 days. Although there was a trend for a better TFR rate for patients treated longer with Imatinib (Figure 1), no significant difference could be observed for molecular relapse within 12 months according to clinical characteristics including age, sex, Sokal risk score, prior IFN, and time to MMR/DMR (Table 1). Ten patients (15%) showed "withdrawal syndrome" which is transitory musculoskeletal pain within several weeks after imatinib discontinuation, and all patients except one recovered without any treatments. Conclusion: According to the A-STIM criteria, around 70% of patients with deep and sustained molecular responses could safely stop imatinib. TFR in this prospective Japanese clinical study was higher than previously reported, probably because there were much more patients who treated with imatinib for longer duration than previous studies. We will report prognostic factors in the exploratory research of JALSG-STIM213 study including T/NK-cell profiling in peripheral blood, BIM deletion polymorphism, and ABCG2 421C/A polymorphism at this ASH meeting. Table 1. Table 1. Figure 1. Figure 1. Disclosures Takahashi: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Otsuka: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Speakers Bureau; Astellas: Speakers Bureau; Masis: Consultancy; Sysmex: Research Funding, Speakers Bureau; BMS: Honoraria, Research Funding, Speakers Bureau. Hatta:CHUGAI PHARMACEUTICAL CO. LTD: Honoraria; Kyowa Hakko Kirin CO., Ltd, Japan: Honoraria; Celgene K.K.: Honoraria. Usuki:Fuji Film RI Pharma: Other: personal fees; Fujimoto Pharmaceutical: Research Funding; Otsuka Pharmaceutical: Research Funding; Eisai: Research Funding; Shionogi: Other: personal fees; MSD: Other: personal fees, Research Funding; Nippon Shinyaku: Other: personal fees, Research Funding; Astellas: Research Funding; Chugai Pharmaceutical: Other: personal fees; Takeda Pharmaceutical: Research Funding; Kyowa Hakko Kirin: Other: personal fees, Research Funding; SymBio Pharmaceutical: Other: personal fees, Research Funding; Sanofi: Other: personal fees, Research Funding; Novartis: Other: personal fees, Research Funding; Boehringer Ingelheim: Other: personal fees, Research Funding; Celgene: Other: personal fees, Research Funding; Sumitomo Dainippon Pharma: Other: personal fees, Research Funding; Taiho Pharmaceutical: Other: personal fees, Research Funding; Shire: Research Funding; GlaxoSmithKline: Other: personal fees, Research Funding; Bristol-Myers Squibb: Other. Kobayashi:Gilead Sciences: Research Funding. Naoe:Otsuka Pharmaceutical Co., Ltd.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Patents & Royalties; Pfizer Inc.: Research Funding; Toyama Chemical CO., LTD.: Research Funding; Nippon Boehringer Ingelheim Co., Ltd.: Research Funding; Astellas Pharma Inc.: Research Funding; Celgene K.K.: Research Funding; FUJIFILM Corporation: Patents & Royalties, Research Funding; Kyowa Hakko Kirin Co., Ltd.: Patents & Royalties, Research Funding.

Abstract: We previously reported that TEL-FGFR3 in a patient with peripheral T-cell lymphoma and AML conferred IL-3 independency to Ba/F3 cells and activates MAPKs, p38, PI3K, Stat3 and Stat5 through its constitutive tyrosine kinase (TK) activity in TEL-FGFR3 transfected Ba/F3 cells (TF-V5). Both FGFR3 TK specific inhibitor SU5402 and PI3K inhibitor LY294002 inhibited cell growth of TF-V5 in a dose dependent manner (IC50=5μM, 10μM respectively). SU5402(25μM) resulted in G1 arrest (90%) and induced 80% of apoptosis to TF-V5 after 24hr. LY294002(50μM) decreased expression of c-Myc, Cyclin D3 and CDK4 in TF-V5 and induced G1 arrest (90%) and apoptosis about 20% to TF-V5 after 24hr. SU5402 completely suppressed expression of Bcl-xL and Bcl-2 after 24hr. LY294002 partially suppressed these expressions. As LY294002 did not affect the phosphorylation of STAT5 and STAT3, we hypothesized that these distinct apoptosis inducing abilities between SU5402 and LY294002 might be caused by the difference of Bcl-xL and Bcl-2 expression levels. Recent report suggests that FGFR3 activates Stat5 through recruitment of Pyk2 (proline-rich tyrosine kinase 2)-Src to its juxta-membrane (JM) domain. Therefore, we examined whether PP1/PP2 which are known as Src kinase inhibitors inhibit TF-V5 cell growth. PP1 and PP2 inhibited TEL-FGFR3 induced cell proliferation in a dose dependent manner (IC50=15μM, 15μM respectively). In contrast, growth of mock with IL-3 was not inhibited at a high concentration of PP1or PP2(30μM). PP1/PP2 did not affect auto-phosphorylation of TEL-FGFR3. Interestingly, PP1/PP2 inhibit Tyr phosphorylation of Pyk2 except Tyr402 and markedly suppressed activation of Stat3, Stat5 without affecting MAPKs and PLC gamma activation. PP1/PP2 suppressed expression of Bcl-xL and Bcl-2 partially but not of Bax and induced apoptosis 20% and 30% respectively. PP1/PP2 partially blocks cell cycle at G1 phase. When TF-V5 was co-treated with PP1(30μM)+LY294002(50μM) or PP2(30μM)+LY294002(50μM), apoptosis was induced in 60–70% of TF-V5 cells which remained at G1 phase after 24hr. Although PP1+LY294002 or PP2+LY294002 did not suppress Bcl-xL and Bcl-2 completely like SU5402, PP1/PP2 induced N-terminal cleavage form of Bax. Conclusion: PP1/PP2 induces apoptosis in TF-V5 by activating Bax and by Pyk2-Src kinase inactivation that leads to the change of Bax/Bcl-2 or Bax/Bcl-XL ratio. Combination of PP1/PP2 and LY294002 induce high rate of apoptosis under G1 arrest in TF-V5 and may represent a novel approach against TEL-FGFR3 associated hematopoietic malignancies.