mounting evidence suggests that the npas2 protein and other circadian genes are involved in tumorigenesis and tumor growth, possibly through their control of cancer-related biologic pathways. a missense polymorphism in npas2 (ala394thr) has been shown to be associated with risk of human tumors including breast cancer. these findings provide evidence suggesting a possible role for the circadian "npas2" gene in cancer prognosis. these results have been confirmed in both breast and colorectal cancers.