A novel, mitochondrial, internal tRNA-derived RNA fragment possesses clinical utility as a molecular prognostic biomarker in chronic lymphocytic leukemia

•A qPCR assay was developed for the quantification of a new mt-tRNA-derived fragment.•i-tRF-PheGAA can distinguish between CLL patients and normal controls.•An association was observed between i-tRF-PheGAA expression and CLL clinical stage.•Patients overexpressing i-tRF-PheGAA show significantly poorer overall survival.•The prognostic power of i-tRF-PheGAA is independent of established prognosticators.