The invention is based on the surprising finding that SIK3 is associated with resistance against anti-tumour immune responses. In particular, the invention provides methods for treating proliferative diseases using inhibitors of SIK3, especially nucleic acid or small molecule inhibitors of SIK3. Also provided are methods of sensitising cells involved with a proliferative disorder against the cytotoxic effect of certain pro-inflammatory signalling pathways, and/or to kill such cells and/or methods for treating proliferative diseases, using a SIK3 inhibitor together with ligands or agonists of such signalling pathways. Other methods provided by the invention include those involving SIK3 inhibitors to enhance or overcome certain side effects associated with treatments that utilise such signalling pathways, as well as diagnostic, prognostic and monitoring methods and kits based on the detection of SIK3 in a sample obtained from a subject, and screening methods useful for identifying or characterising inhibitors of SIK3.
