Monoclonal B-cell lymphocytosis; not the same as B-cell chronic lymphocytic leukaemia.

INTRODUCTION: Depending on the location and the extent of disease, mature B-cell disorders can be divided into benign monoclonal B-cell lymphocytosis (MBL), chronic lymphocytic leukaemia (CLL) and small lymphocytic lymphoma (SLL). Whereas SLL is characterised by its location outside the blood stream, MBL is distinguished from CLL by a monoclonal B-cell count below 5 × 109/l. Due to its low tendency to transform into CLL, correct diagnosis of MBL is essential. We hypothesised that this might not always be the case. METHODS: This study includes data on monoclonal B-lymphocyte count based on diagnostic flow cytometry from patients diagnosed in the period from 1 January 2011 to 31 December 2016 at the Department of Haematology, Aarhus University Hospital, Denmark. A total of 69 patients had less than 5 × 109/l monoclonal B-cells with a CLL-like immunophenotype in peripheral blood. All cases were classified based on the 2008 WHO criteria and evaluated according to the clinical diagnosis of CLL, MBL or SLL in the medical records. A total of 24 of the 69 patients were classified as MBL. RESULTS: In the study cohort, 12 (50%) patients classified as MBL were diagnosed accurately with MBL, whereas nine (38%) were diagnosed with CLL. CONCLUSIONS: The findings of this study indicate that a sizeable fraction of MBL patients are diagnosed inaccurately with CLL, even after the introduction of the MBL diagnosis. FUNDING: The Danish Cancer Society. TRIAL REGISTRATION: not relevant.

Combination of RNA- and exome sequencing: Increasing specificity for identification of somatic point mutations and indels in acute leukaemia.

Handling of large data sets from whole exome sequencing is a challenge, not the least because of the high risk of detecting false positive variants. Furthermore, there is still no consensus regarding what stage filtering of variants is performed in the bioinformatics pipeline to produce consistent result sets, the extent of filtering and how this is most optimal performed. We hypothesized that combination of coding transcriptome and exomes enables precise identification of both somatic single nucleotide and indel variants early in the bioinformatics process, superseding the need for extensive annotation and validation from external databases. Exome and RNA-sequencing were performed on diagnosis-remission paired bone marrow samples from 5 cytogenetically normal AML, i.e. sequencing of 20 samples in total. Intersection of rare exome and RNA variants, exclusively found in the diagnostic samples, yielded a median of 6 somatic point mutations and small indels, ranging from 3 to 21. Close correlation between routine diagnostic biomarkers was observed in 29/30 laboratory tests, with the exception of a large FLT3 internal tandem repeat, whereas WT1 with nonsense mutation lacked RNA transcripts. Additionally, the assay revealed mutations in DNMT3A, IDH2, TET2 and IL32 frame shift, not encompassed by routine panel. We thus describe a procedure to effectively reduce observations to a focused subset of high specificity. The approach is applicable to precise screening of both putative driver mutations and, often heterogeneous, discrete patient specific somatic combinations.