The methods of the present disclosure are directed toward methods of diagnosis and treatment of cancer in a subject. The present disclosure provides methods of diagnosing abnormal cells in a subject by measuring the level of Hexim-1 in a sample from the subject, where elevated levels of Hexim-1 indicate abnormal cells. This disclosure further provides methods of treating cancer or hyperplasia, comprising administering to a subject in need thereof a therapeutically effective amount of Hexim-1 or an activator of Hexim-1 expression or activity.