Clinical Utility of Hematopathologist-Triaged NGS Testing When Investigating Patients with Suspected MDS

The recognition of MDS is challenging in early stages, where diagnosis may rely solely upon morphological criteria for dysplasia, a non-specific finding prone to inter-observer variation. Patients with equivocal bone marrow (BM) findings may be discharged from Hematology clinics and lost to follow up, or subjected to serial, invasive BM investigations and diagnostic delays. We therefore aimed to demonstrate the importance of hematopathologist-triaged, targeted NGS in identifying clonal cytopenias of undetermined significance (CCUS) in cases where MDS diagnostic criteria are not met based on morphology or cytogenetic analysis. We explored this using three REB-approved cohorts. Our first cohort was retrospective with BM samples ranging from 2010-14, involving cases that were previously suspicious for but non-MDS diagnostic. This included 70 patients from Sunnybrook (SHSC) and Kingston Health Sciences Centres (KHSC): 16 age-matched controls (8 negative lymphoma staging, 8 non-MDS cytopenias); 18 suspicious for MDS; 20 MDS; and 16 MDS/MPN. DNA was extracted and NGS was performed using our custom 48-gene Ion Torrent AmpliSeq myeloid panel (ThermoFisher). We identified suspected mutations in 2/16 (13%) controls (i.e. CHIP), 12/18 (67%) suspicious cases, 17/20 (85%) MDS cases, and 16/16 (100%) MDS/MPN cases. The mean and median number of mutations per suspicious patient (respectively 0.89 and 1; most commonly in SF3B1, TET2, RUNX1, and ASXL1) were lower than MDS (1.85 and 2; p=0.011) and MDS/MPN (3.13 and 3; p