In this review, we introduce a new vision of cancer describing opposing effects that control progression. Cancer is a paradigm of opposing of "Yin" and "Yang," with Yin being the effect to promote cancer and Yang that to maintain the normal state. This Yin Yang hypothesis has been used to select Yin and Yang genes to develop multigene signatures for determining prognosis in lung and breast cancer. Most of the Yin genes are involved in cell survival, growth, and proliferation, whereas most Yang genes are involved in cell apoptosis. Furthermore, Yin and Yang pathways have been identified in breast cancer and compounds that can inhibit the Yin pathways or activate the Yang pathways have been examined, suggesting a new promising targeting therapy for cancer. We are building a Yin Yang model to represent the dynamic change of Yin and Yang genes and pathways.