The present invention relates to the use of pituitary tumor transforming gene 1 (PTTG1) as a biomarker for diagnosing cancer as well as for determining cancer treatment responsiveness. In one embodiment, the present invention provides a method of treating cancer by inhibiting the expression of PTTG1, and administering a therapeutically effective amount of Aurora kinase inhibitor, HDAC inhibitor and/or ROS-generating agent.
