Actions of many herbal medicine products for cancer treatment are linked to an altered production of TGF-β in the target cells. An altered TGF-β production in the target cells will have profound effects on the patients. Therefore, it is important that we review the pros and cons of these products on cancer development and progression in terms of TGF-β signaling. It has been well established that TGF-β is growth inhibitory to benign cells or early stages of cancer cells but it is tumor promoting and metastatic for advanced malignancies. Further, many dietary components can alter gene-specific DNA methylation levels in systemic and in target tissues. Since TGF-β signaling in cancer is closely linked to the DNA methylation profiles, we also review the effect of dietary components on DNA methylation. In light of this knowledge, it is important to note that many natural products that can induce TGF-β production in the target cells may be beneficial in preventing cancer development but may be harmful for cancer patients, especially when they harbor advanced stage cancer. A discussion of the effect of herbal natural products on cancer can be divided into three categories. The first category of herbal medicine products will be those related to the induction of cancer as far as TGF-β is concerned. Since TGF-β is growth inhibitory and pro-apoptosis to benign cells, any herbal medication that can induce the production of TGF-β in the target cells will be beneficial to the patients. However, such herbal medicine may not necessarily be beneficial for patients with established and advanced cancer. The second category of herbal products will inhibit TGF-β signaling and will reduce TGF-β mediated growth promotion and metastasis in advanced cancers. For patients with established and advanced cancer, agents that can inhibit the production of TGF-β may also inhibit cancer growth and metastasis. Finally, the third category of herbal products has no impact on TGF-β signaling, such as lycopene.