Methods and compositions for treating and diagnosing cancer and screening for agents for such treatment and diagnosis are provided. The methods involve screening for agents that modulate the activity or expression of FOXM1, which has been discovered herein to play a role in cell growth and cell cycle regulation. Methods for treating cancer, methods for modulating the activity or expression of FOXM1, methods for diagnosing a subject that has or is at risk of developing cancer, and pharmaceutical compositions are also provided.