Provided are methods and compositions for the treatment of cancers associated with overexpression of a BCL2 gene and/or gene product in a subject, and methods and compositions for the improvement of anti-cancer therapy, such as chemotherapy and radiation therapy. Also provided are methods for determining the efficacy of a cancer therapy in a subject, methods for diagnosing cancer, methods for assessing patient prognosis, and methods for inducing apoptosis of a cell.