Abstract
In recent years, a subgroup of B-cell precursor acute lymphoblastic leukemia (BCP ALL) without an established abnormality ("B-other") has been shown to be characterized by rearrangements of ABL1, ABL2, CSF1R, or PDGFRB (a.k.a. ABL-class genes). Using FISH with probes for these genes, we screened 55 pediatric and 50 adult B-other cases. Three (6%) of the adult but none of the childhood B-other cases were positive for ABL-class aberrations. RT-PCR and sequencing confirmed a rare SFPQ-ABL1 fusion in one adult B-other case with t(1;9)(p34;q34). Only six SFPQ-ABL1-positive BCP ALLs have been reported, present case included. A review of these shows that all harbored fusions between exon 9 of SFPQ and exon 4 of ABL1, that the fusion is typically found in adolescents/younger adults without hyperleukocytosis, and that IKZF1 deletions are recurrent. The few patients not treated with tyrosine kinase inhibitors (TKIs) and/or allogeneic stem cell transplantation relapsed, strengthening the notion that TKI should be added to the therapy of SFPQ-ABL1-positive BCP ALL.
Highlights
B-cell precursor acute lymphoblastic leukemias (BCP ALL) without any established abnormalities, such as characteristic fusion genes and ploidy groups, are often denoted B-other.[1]
Of the three ABL-class-positive adult cases identified, one had a t (1;5)(q22;q33) involving the CSF1R gene and this case has previously been reported to harbor an MEF2D-CSF1R fusion that was responsive to imatinib.[17]
No RNA was available for RNA sequencing and, the partner gene could not be ascertained. Because this patient was diagnosed in the pre-tyrosine kinase inhibitors (TKI) era (2001), no action could be taken based on these FISH results
Summary
B-cell precursor acute lymphoblastic leukemias (BCP ALL) without any established abnormalities, such as characteristic fusion genes and ploidy groups, are often denoted B-other.[1]. We used FISH to ascertain ABL-class rearrangements in a series of B-other cases from a single center and here report their frequencies in such a cohort and summarize the genetic and clinical features of BCP ALL cases with the rare SFPQ-ABL1 fusion reported to date.
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