Objective: To investigate the clinical features of adult B-cell acute lymphoblastic leukemia (B-ALL) with E2A-PBX1 fusion gene positive. Methods: The clinical data of 91 Philadelphia chromosome negative B-ALL patients who received chemotherapy regularly in Nanfang Hospital of Southern Medical University from March 2015 to December 2017 were collected. According to the fusion gene detection results, the patients were divided into E2A-PBX1 fusion gene positive group and E2A-PBX1 fusion gene negative group. The clinical features and prognosis of both groups were retrospectively analyzed. And then E2A-PBX1 fusion gene negative group was further divided into MLL-AF4 fusion gene positive group and the other ALL groups,which were compared with E2A-PBX1 fusion gene positive group in the prognosis. Results: There were 11 ALL patients with E2A-PBX1 fusion gene positive, and 80 ALL patients with E2A-PBX1 fusion gene negative. The level of lactic dehydrogenase (LDH) in E2A-PBX1 fusion gene positive group was higher than that in E2A-PBX1 fusion gene negative group [4 063 U/L (1 070- 9 554 U/L) vs. 454 U/L (103- 18 651 U/L), U=-4.700, P < 0.01], and there were no statistically significant differences in age, gender, white blood cell count and extramedullary invasion (all P > 0.05). The immunophenotypes of ALL patients with E2A-PBX1 fusion gene positive were all common B-cell phenotype. Out 4 of 7 ALL patients showed the different expression of Philadelphia-like ALL phenotype CRLF2 or phosphorylated CRKL or phosphorylated STAT5 by using flow cytometry. The complete remission (CR), minimal residual disease (MRD)-negative and the recurrence for 11 cases of E2A-PBX1 fusion gene positive group included 9, 7, 8 cases, respectively after first course of induction chemotherapy. The CR, MRD-negative and the recurrence for 80 cases of E2A-PBX1 fusion gene negative group included 71, 53, 26 cases, respectively after the first course of induction chemotherapy. There were no statistically significant differences in the CR and MRD-negative between the two groups after the first course of induction chemotherapy (P= 0.721, P= 0.487), but there was a statistical difference in the recurrence (χ²= 7.751, P= 0.012). The median follow-up time was 17 months (1-44 months), and the 1-year overall survival (OS) rate and 1-year event-free survival (EFS) rate of E2A-PBX1 fusion gene positive ALL group were lower than those of the negative group (OS: 43.6% vs. 70.0%, P= 0.020; EFS: 13.6% vs. 60.0%, P= 0.002). Subgroup analysis showed that there were no statistical differences between E2A-PBX1 fusion gene positive group and MLL-AF4 fusion gene positive group in 1-year OS rate and 1-year EFS rate (P= 0.617, P= 0.984). Conclusions E2A-PBX1 fusion gene positive rate is low in adult B-ALL patients with a good response to traditional chemotherapy in the early stage, but its cumulative recurrence rate is high. It is a high-risk cytogenetic abnormality which is similar to MLL gene rearrangement and needs to explore novel therapy strategies.

Objective:To establish a screening system of adult Philadelphia chromosome-like acute lymphoblastic leukemia (Ph-like ALL) by fluorescence in situ hybridization (FISH) .Method:Based on the genetic characteristics of Ph-like ALL, FISH probes were designed for ABL1, ABL2, JAK2, EPOR, CRLF2, CSF1R, PDGFRB, and P2RY8 gene breakpoints, which were used to screen Ph-like ALL in B-ALL patients without BCR-ABL1, ETV6-RUNX1, MLL, and E2A gene arrangement. Furthermore, it was analyzed in combination with flow immunophenotype, next-generation sequencing for targeted gene mutations, and RNA sequencing (RNA-seq) .Results:A total of 189 adult B-ALL patients diagnosed in Nanfang Hospital from January 2016 to April 2019 were enrolled in this study. Using FISH and/or PCR, BCR-ABL1, ETV6-RUNX1, MLL, or E2A arrangement was detected in 83 of them, and Ph-like ALL was detected by FISH in the other 106, resulting in the presence of typical gene arrangements of Ph-like ALL in 12 patients (11.3% , 12/106) . Validated by RNA-seq, the sensitivity and specificity of FISH for Ph-like ALL were 71.4% and 95.8% , respectively. After further analysis with immunophenotype, targeted gene mutations, and RNA-seq, 14 (13.2% , 14/106) were diagnosed with Ph-like ALL.Conclusion:This data shows high specificity of FISH for identification of Ph-like ALL and combining immunophenotype and sequencing technology can improve the diagnostic system.