The invention provides methods for inhibiting tumor cell proliferation by inhibiting FoxM1B activity, expression, or nuclear localization in a tumor cell. The invention also provides methods for preventing tumor progression in an animal comprising inhibiting FoxM1B activity, expression, or nuclear localization. Furthermore, the invention provides methods for inhibiting tumor cell growth in an animal comprising inhibiting FoxM1B activity, expression, or nuclear localization in tumor cells in the animal.