RESULTS
A 19-month-old female with right facial nerve palsy was referred to the University of Tokyo Hospital. She had no personal or family history of cancer. Magnetic resonance imaging revealed a tumor lesion that filled the right temporal bone (Fig. 1A). Enhanced computed tomography showed bilateral renal involvement (Fig. 1B). Lymph nodes and the thymus were intact. Biopsy of the tumor tissue revealed DLBCL consisting of diffuse proliferation of centroblasts (Figs. 1C­–F). The tumor infiltrated the central nervous system and was diagnosed as Murphy stage IV DLBCL. BM samples aspirated from the bilateral ilia showed normal karyotype and no morphological evidence of tumor invasion.
She was administered short-pulse intensive chemotherapy to treat mature B-cell lymphoma.15 Cytology of the cerebrospinal fluid was normal one month after initiating chemotherapy. The tumor nearly dissolved after chemotherapy, except for a small residual lesion in the right mastoid observed by gadolinium enhancement magnetic resonance imaging. Although discharged seven months after diagnosis, leukocytosis with blast cells in peripheral blood developed 2 months after completion of the chemotherapy. Flow cytometry showed abnormal lymphocytes with characteristics of the mature B-lineage (CD10+, CD19+, and CD20+, partially positive for immunoglobulin light chain lambda, and CD34-) in the BM. G-banding analysis and fluorescence in situ hybridization showed addition of 11q23 and KMT2A rearrangement, respectively. RT-PCR confirmed the presence of the KMT2A -MLLT3 fusion not only in sample at the recurrent timepoint, but also in that upon initial presentation, which demonstrated normal morphology and karyotype. Since leukocytosis worsened after reinitiating ALL-specific chemotherapy,16 she underwent hematopoietic cell transplantation during non-remission that resulted in the expansion of blast cells after neutrophil engraftment. She continued palliative chemotherapy with bortezomib. Unfortunately, the disease progressed and she died 18 months after diagnosis.
RNA-seq on BM during recurrent cancer identified theKMT2A -MLLT3 fusion including exons 1–9 and 6–11 ofKMT2A and MLLT3 , respectively, which was validated by Sanger sequencing (Figs. 2A–B). Other fusions, such asIGH -BCL6 , IGH -BCL2 , andIGH -MYC , were not detected and no mutations were found inKRAS , NRAS , PTPN11 , and FLT3 . ITD and the N676 and D835 variants of FLT3 were not identified by RT-PCR and Sanger sequencing of the primary or recurrent BM.
MEIS1 and MEF2C , which are highly expressed inKMT2A -rearranged leukemia,17 were overexpressed in the BM during cancer recurrence (60 and 83 FPKM, respectively); however, expression of posterior HOXA genes (HOXA6 ,7 , 9 , and 10 ), also upregulated inKMT2A -rearranged leukemia, were not detected. IGLL5levels, involved in the expression of IGLJ1 and IGLC1 , were elevated (400 FPKM), whereas the expression of CD34 andDNTT (encoding terminal deoxynucleotidyl transferase) was not elevated (0.11 and 0.80 FPKM, respectively). t-SNE plots showed that our patient formed a part of the KMT2A -rearranged ALL, but not DLBCL, cluster (Fig. 2C).