The invention relates to a pharmaceutical composition comprising a combination of a compound of formula (I) or a pharmaceutically acceptable salt thereof, and at least one second agent selected from the group consisting of signal transduction pathway inhibitors, tumour immunotherapeutics, agents inhibiting the BCL2 family of proteins, agents inhibiting Mcl-1, proteasome Inhibitors, poly (ADP-ribose) polymerase (PARP) Inhibitors, aromatase inhibitors, conventional cytotoxic agents or a miscellaneous agent selected from abiraterone, ARN-509 and MYC inhibitors.