BCOR Mutations in Acute Myeloid Leukemia: Clonal Evolution and Prognosis

Background

BCOR gene is a transcription repressor that may influence normal hematopoiesis and is associated with poor prognosis in acute myeloid leukemia (AML) with normal karyotype. However, due to the rare mutation frequency in AML (3.8%-5%), clinical characteristics and prognosis of AML patients with BCOR mutation including abnormal karyotype are still unknown. In addition, the clonal evolution of AML patients with BCOR mutation has not been fully investigated.

Methods

By means of next generation of sequencing, we performed sequencing of 114 genes related to hematological diseases including BCOR on 509 newly diagnosed AML patients (except for acute promyelocytic leukemia) from March 2017 to April 2019. The 2017 European Leukemia Net (ELN) genetic risk stratification was used to evaluate prognosis. Overall survival (OS) was defined as the time from diagnosis to death or last follow-up. Relapse-free survival (RFS) was measured from remission to relapse or death. Clonal evolution was investigated through analyzing bone marrow samples at diagnosis, complete remission (CR) and relapse from the same patient.

Result

Among 509 AML patients, we found BCOR mutations in 23 patients (4.5%). BCOR mutations were enriched in patients with mutations of RUNX1 (p = 0.008) and BCORL1 (p = 0.0003). Patients with BCOR mutation were more at adverse ELN risk category compared to patients without BCOR mutation (p = 0.007). Besides, there was a larger proportion of patients with normal karyotype in BCOR mutation group but it had not reached statistical difference (62.5% vs 45.5%, p = 0.064). The abnormal karyotype in patients with BCOR mutations included trisomy 8, t(9;11), inv(3), -7 and complex karyotype.There were no significant differences in age, sex, white blood cell count, hemoglobin or platelet count between the two groups. More patients died during induction (13.0% vs 3.5%, p = 0.56) and fewer patients achieved CR after 2 cycles of chemotherapy when patients had BCOR mutations (69.6% vs 82.5%, p = 0.115) but the difference had not reached statistical difference . Patients with BCOR mutations had inferior 2-year OS (52.1% vs 70.7%, p = 0.0094) and 2-year RFS (29.8% vs 61.1%, p = 0.0090). After adjustment for ELN risk stratification, BCOR mutation was still remain a poor prognostic factor. However, the adverse prognostic impact of BCOR mutation is overcome by hematopoietic stem cell transplantation (HSCT), in which there was no difference between BCOR mutation group and wild type group (p = 0.474) (Figure 1). Through analysis of paired bone marrow sample at diagnosis, remission and relapse, we revealed the clonal evolution that BCOR mutation was only detected at diagnosis sample as a subclone and diminished at CR and relapse while TP53 mutation was only detected at relapse with a variant allele frequency (VAF) of 25.5%. We also found BCOR mutation at another patient’s diagnosis and relapse sample while TP53 mutation was detected at relapse with VAF of 11.8%.

Conclusion

BCOR is associated with RUNX1 mutation and higher ELN risk. AML patients with BCOR mutation including normal and abnormal karyotype conferred a worse impact on OS that can be overcome by HSCT. BCOR mutation is a subclone at diagnosis or relapse in some patients, in which TP53 mutation clone occurred at relapse.