The present invention relates to microRNAs (miRNAs) which are associated with cancer, particularly including hematologic malignancies, and particularly T-cell acute lymphoblastic leukemia (T-ALL), and to the assessment and modulation thereof in the treatment and management of cancer. The present invention is directed to methods and compositions for diagnosing and treating cancer, particularly T-ALL, by modulating miRNAs, and the use of miRNAs and antagonists thereof, particularly antagomirs, for predicting and assessing response to treatment, in assays for isolating and selecting antagonists, and as compositions for the treatment and management of cancer. Methods and compositions are provided for treatment or alleviation of cancer, particularly T-ALL, with antagonists/antagomirs of miRNAs, particularly one or more of miR-19b, miR-20a, miR26, miR92, miR148 and miR223.