The present invention relates to combination of a BTK inhibitor and an inhibitor of CDK9 for use in the treatment of cancer in a subject. The BTK inhibitor can be acalabrutinib, ibrutinib, or ONO/GS-4059; and the inhibitor of CDK9 can be AZD4573, BAY-1251152, BAY- 1143572, CYC065, alvocidib, AT7519, voruciclib, roniciclib, or dinaciclib.