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).