Cancer remains one of the leading causes of death worldwide and continues to represent a major challenge for modern medicine. While conventional treatments such as surgery, chemotherapy, radiation therapy, and immunotherapy have significantly improved survival and quality of life for many patients, scientific research is increasingly exploring complementary and supportive strategies that may strengthen the overall approach to cancer. Among these, naturally occurring plant compounds known as polyphenols—and particularly flavonoids—have attracted growing interest due to their biological activity and their interaction with multiple cancer-related pathways.
Polyphenols are a broad and diverse group of bioactive molecules that are abundantly found in fruits, vegetables, herbs, teas, cocoa, wine, and many medicinal plants. They play important roles in plant defense and pigmentation and, when consumed by humans, interact with numerous cellular processes. Flavonoids, one of the main subclasses of polyphenols, include compounds such as quercetin, catechins, anthocyanins, kaempferol, and hesperetin. These molecules have been widely studied because they are a regular part of the human diet and generally exhibit low toxicity in normal cells.
To understand why polyphenols are relevant in oncology research, it is important to briefly consider how cancer develops. Cancer arises when normal cells accumulate genetic and molecular alterations that disrupt the balance between cell growth and cell death. These changes may be driven by chronic inflammation, oxidative stress, environmental exposures, radiation, infections, and lifestyle-related factors. As a result, cancer cells acquire the ability to proliferate uncontrollably, resist programmed cell death, alter their metabolism, stimulate the formation of new blood vessels, evade immune detection, and spread to other tissues.
Figure 1. plant-derived polyphenols highlighting representative flavonoids commonly studied in cancer research.
One of the earliest areas of interest in polyphenol research is their relationship with oxidative stress. Oxidative stress occurs when reactive oxygen species, commonly known as free radicals, overwhelm the cell’s antioxidant defenses. This imbalance can damage DNA, proteins, and cellular membranes, contributing to cancer initiation and progression. Polyphenols are well known for their antioxidant properties, as they can neutralize free radicals and help protect cellular structures from oxidative damage. By reducing oxidative stress, these compounds may contribute to maintaining genomic stability and overall cellular health.
Interestingly, polyphenols do not act exclusively as antioxidants. In cancer cells, some polyphenols may behave as pro-oxidants, increasing oxidative stress beyond a level that malignant cells can tolerate. Cancer cells often already exist under higher levels of oxidative stress compared to normal cells, making them more vulnerable to additional increases in reactive oxygen species. This selective vulnerability is one of the reasons polyphenols are being studied for their potential influence on cancer cell survival without significantly affecting healthy tissue.
Another important area of research focuses on apoptosis, or programmed cell death. In healthy tissues, apoptosis acts as a natural quality-control mechanism that eliminates damaged or abnormal cells. Cancer cells frequently evade apoptosis, allowing them to survive despite substantial genetic damage. Research suggests that flavonoids may help reactivate apoptotic pathways in cancer cells by influencing key signaling molecules and gene expression. Through this mechanism, polyphenols may contribute to the selective elimination of malignant cells.
Uncontrolled cell division is a defining characteristic of cancer, and polyphenols have also been shown to influence the cell cycle. The cell cycle is a tightly regulated process that controls cell growth and division. Many flavonoids have demonstrated the ability to slow or halt the cell cycle at specific phases, reducing abnormal proliferation. By interfering with signaling pathways that drive uncontrolled cell division, polyphenols may help limit tumor growth and progression.
As tumors grow, they need to develop their own blood supply to obtain oxygen and nutrients. This process, known as angiogenesis, is essential for tumor survival and expansion. Cancer cells release signaling molecules that stimulate the formation of new blood vessels. Scientific studies indicate that certain polyphenols may interfere with angiogenic signaling, potentially limiting the tumor’s ability to sustain itself. By affecting angiogenesis, these compounds may also influence the tumor’s ability to invade nearby tissues and metastasize to distant organs.
Metastasis, which is the spread of cancer cells from the primary tumor to other parts of the body, is responsible for the majority of cancer-related deaths. Research suggests that polyphenols may influence processes involved in cell migration, invasion, and tissue remodeling. By modulating enzymes and signaling pathways that cancer cells use to penetrate surrounding structures, polyphenols may help reduce metastatic potential in experimental settings.
Chronic inflammation is now recognized as a key factor in cancer development and progression. Inflammatory signaling can promote DNA damage, support tumor growth, and create a microenvironment that facilitates cancer cell survival. Many polyphenols possess anti-inflammatory properties and have been shown to modulate key inflammatory pathways, including those involving cytokines and transcription factors such as NF-κB. By reducing inflammation, polyphenols may help shift the tumor microenvironment toward conditions that are less favorable for cancer growth.
Another emerging area of interest is cancer metabolism. Cancer cells often rely on altered metabolic pathways, such as increased glucose uptake and aerobic glycolysis, to sustain rapid growth and survival. Some flavonoids have been shown to influence metabolic enzymes and mitochondrial function, potentially altering the energy production strategies used by cancer cells. This metabolic vulnerability represents a promising target in modern oncology research.
Polyphenols are also being investigated for their potential to support conventional cancer treatments. Preclinical studies suggest that these compounds may increase sensitivity to chemotherapy or radiation therapy in certain contexts, while also helping protect normal cells from treatment-induced damage. Additionally, some research indicates that polyphenols may help address treatment resistance, one of the major challenges in oncology. However, these interactions are complex and depend heavily on dosage, timing, and individual patient characteristics.
Figure 2. how polyphenols are studied in cancer prevention, treatment-related pathways, and supportive cancer care.
Despite their potential, polyphenols present several challenges when considered for clinical use. One important limitation is bioavailability, meaning the extent to which these compounds are absorbed, distributed, and retained in the body. Many polyphenols are rapidly metabolized and eliminated, which can limit their effectiveness. Ongoing research is focused on improving delivery methods, formulations, and combination strategies to enhance their biological impact.
It is essential to emphasize that polyphenols and flavonoids are not cures for cancer and should not be considered substitutes for standard medical treatments. Instead, they should be understood as biologically active compounds that may support broader, evidence-based approaches to cancer care, always under appropriate medical supervision.
As oncology research continues to evolve, polyphenols represent an important area of study within integrative and precision oncology. Their ability to interact simultaneously with multiple cancer-related pathways makes them particularly compelling in a disease as complex and multifactorial as cancer. Ongoing scientific and clinical studies will continue to clarify how these compounds can be incorporated more effectively and safely into comprehensive cancer care strategies.
Main reference:
Hazafa, A., Rehman, K. U., Jahan, N., & Jabeen, Z. (2020). The Role of Polyphenol (Flavonoids) Compounds in the Treatment of Cancer Cells. Nutrition and cancer, 72(3), 386–397. https://doi.org/10.1080/01635581.2019.1637006
Other references:
Millimouno, F. M., Dong, J., Yang, L., Li, J., & Li, X. (2014). Targeting apoptosis pathways in cancer and perspectives with natural compounds from mother nature. Cancer prevention research (Philadelphia, Pa.), 7(11), 1081–1107. https://doi.org/10.1158/1940-6207.CAPR-14-0136
Block, K. I., Gyllenhaal, C., Lowe, L., Amedei, A., Amin, A. R. M. R., Amin, A., Aquilano, K., Arbiser, J., Arreola, A., Arzumanyan, A., Ashraf, S. S., Azmi, A. S., Benencia, F., Bhakta, D., Bilsland, A., Bishayee, A., Blain, S. W., Block, P. B., Boosani, C. S., Carey, T. E., … Zollo, M. (2015). Designing a broad-spectrum integrative approach for cancer prevention and treatment. Seminars in cancer biology, 35 Suppl(Suppl), S276–S304. https://doi.org/10.1016/j.semcancer.2015.09.007
Vauzour, D., Rodriguez-Mateos, A., Corona, G., Oruna-Concha, M. J., & Spencer, J. P. (2010). Polyphenols and human health: prevention of disease and mechanisms of action. Nutrients, 2(11), 1106–1131. https://doi.org/10.3390/nu2111106
