Genetic features of precursor B‐cell phenotype Burkitt leukemia with IGH‐ MYC rearrangement

BACKGROUND: An atypical form of Burkitt leukemia/lymphoma (BL), BL with a phenotype of precursor B‐cells (preBLL), is listed in the WHO Classification. Recent reports suggested that preBLL and classical BL could be distinguished by the differences in IG‐MYC translocation architecture and an additional mutated genes profile. The characteristics of classical BL are IG‐MYC by aberrant somatic hypermutation or class switch recombination, and BL‐specific gene mutations such as MYC, ID3, and CCND3. Meanwhile, preBLL is characterized by IG‐MYC due to aberrant VDJ recombination and mutations in NRAS and KRAS. However, it is not clear whether all preBLL cases can be differentiated. This report investigated the molecular characteristics of an infant preBLL case, with a more advanced stage of maturity than typical preBLL. CASE: The patient showed BL‐like morphology with IGH‐MYC rearrangement. In the immunophenotyping, CD20 and surface immunoglobulin were negative, whereas other markers were consistent with BL. To evaluate the genetic contribution, we performed whole‐exome sequencing. The breakpoint analysis revealed the IG‐MYC occurred due to an aberrant VDJ recombination. Meanwhile, additional somatic mutations were detected in FBXO11, one of the mutant genes specific to BL. In the analysis of the specimen in complete remission, mutation in KRAS, frequently mutated in preBLL, was detected with low frequency, suggesting somatic mosaicism. CONCLUSION: The present case showed the characteristics of both typical preBLL and classical BL. Because preBLL includes atypical cases such as the present case, further studies are required to elucidate preBLL features.