Genetic features of B‐cell lymphoblastic lymphoma with TCF3‐PBX1

BACKGROUND: Lymphoblastic lymphoma (LBL) and acute lymphoblastic leukemia (ALL) are categorized as the same entity under precursor lymphoid neoplasms in the World Health Organization classification. However, compared to B‐cell ALL, the molecular genetic makeup of B‐cell LBL remains to be understood, mainly due to its rarity. We performed whole exome sequencing (WES) on seven patients with TCF3‐PBX1‐positive B‐cell LBL. METHODS: WES was performed using DNA extracted from tumor specimens and paired blood samples at remission for six patients, and tumor‐only analysis was performed for one patient whose remission sample was not available. For one patient, a relapsed sample was also analyzed. RESULTS: KMT2D variants and 6q LOH were found as recurrent alterations. Somatic variants of KMT2D were identified in three of the seven patients. Of note, the two patients with heterozygous nonsense variant of KMT2D were at stage III, without bone marrow infiltration. 6q LOH was also identified in two others, out of the seven patients. The common 6q deleted region of the two patients ranged from 6q12 to 6q16.3. Both patients had bone marrow infiltration. Analysis of recurrent case also revealed that the relapsed clone might be derived from a minor clone of the bone marrow at diagnosis. CONCLUSION: In this study, through WES for seven patients with TCF3‐PBX1‐positive B‐LBL, we identified KMT2D mutations and 6q LOH as recurrent alterations. In order to elucidate the relationship between these recurrent alterations and disease specificity or outcomes, further studies comparing with TCF3‐PBX1‐positive B‐ALL are required.