Quercetin and Cancer: A Natural Ally for Anticancer, Antioxidant, Antiviral, and Anti-Inflammatory

Discover how this powerful plant compound may help change cancer pathways, reduce histamine overload, and support your body’s immune resilience—backed by peer-reviewed science.

Researched and written by Keith Bishop, Clinical Nutritionist, Cancer Coach, Retired Pharmacist, and Founder of Prevail Over Cancer.

Quercetin is a plant-derived flavonol found in many fruits, vegetables, and herbs. Known for its potent antioxidant, anti-inflammatory, antihistamine, and anticancer properties, it’s emerging as a key player in integrative oncology and immune modulation.

If you’re navigating cancer—whether newly diagnosed, in treatment, or in recovery—you’ve likely heard about antioxidants and immune support. But one compound stands out: quercetin, a flavonoid found in everyday foods like onions, apples, and broccoli. Emerging research suggests quercetin may help regulate inflammation, stabilize histamine levels, and even influence cancer-related pathways like apoptosis and angiogenesis. In this guide, we’ll explore how quercetin works, which foods are richest in it, and how enhanced absorption strategies like Pathway-2™ Protisorb™ may improve its impact—so you can make informed, science-backed choices on your healing journey.

Quercetin Anticancer Mechanisms

Quercetin exerts anticancer effects through multiple cellular pathways. It inhibits tumor proliferation, invasion, and metastasis by modulating:

• Apoptotic signaling (p53, Caspase-3)
• Inflammatory pathways (NF-κB, MAPK)
• Cell cycle regulation (PI3K/AKT, Wnt/β-catenin)
• Non-coding RNAs that influence tumor suppressor and oncogenic gene expression

In neuroglioma models, quercetin nanoparticles induced apoptosis and autophagy via LC3/ERK/Caspase-3 activation and AKT/mTOR inhibition.[i]

Cancers Studied with Quercetin

Quercetin was found to induce the apoptosis of all the tested laboratory cancer cell lines and animals at the utilized concentrations.

• Colon carcinoma[ii]
• Prostate cancer[iii]
• Breast cancer[iv]
• Acute lymphoblastic leukemia (ALL)[v]
• Multiple myeloma[vi]
• Lymphoma[vii]
• Ovarian cancer[viii]
• Pheochromocytoma[ix]
• Gastric cancer[x] (stomach cancer)[xi]
• Neuroglioma (brain cancer models)[xii]

Quercetin Antihistamine & Anti-Inflammatory Effects

Quercetin stabilizes mast cells and inhibits histamine release, making it a natural antihistamine. It also downregulates inflammatory cytokines like IL-6 and TNF-α, offering relief for allergy sufferers and chronic inflammatory conditions.[xiii]

Quercetin Antioxidant Defense

Quercetin scavenges free radicals and protects against oxidative stress by:

• Donating electrons to neutralize reactive oxygen species (ROS)
• Upregulating endogenous antioxidant enzymes like SOD and catalase
• Preserving mitochondrial integrity and reducing DNA damage

These antioxidant effects are foundational to its role in cancer prevention and neuroprotection.[xiv] [xv]

Antiviral Actions of Quercetin

Quercetin has demonstrated broad-spectrum antiviral activity across multiple virus families, making it a promising candidate for integrative immune support. Mechanistically, quercetin interferes with viral entry, replication, and protein processing. For example, it inhibits SARS-CoV-2 infection by blocking syncytium formation and suppressing furin-mediated cleavage of the spike protein, thereby reducing viral propagation in human cells.[xvi] [xvii]

Beyond coronaviruses, quercetin has shown inhibitory effects against Epstein-Barr virus (EBV)[xviii], influenza (H1N1)[xix], hepatitis C virus (HCV)[xx], herpes simplex virus (HSV)[xxi], and HIV[xxii] by targeting viral proteases and modulating host inflammatory responses. Its ability to synergize with conventional antivirals may also reduce drug toxicity and enhance therapeutic outcomes. These findings position quercetin as a versatile antiviral agent with potential applications in both prevention and adjunctive therapy.

Top 10 Quercetin-Rich Foods

Here are the most concentrated dietary sources of quercetin:

Enhancing Quercetin Absorption: Pathway-2™ Protisorb™

Quercetin’s bioavailability is notoriously low due to poor water solubility and rapid metabolism. That’s where Pathway-2™ Protisorb™ comes in.

Developed by Ultra Botanica, Pathway-2™ uses a brown rice protein scaffold to deliver quercetin and curcumin in a bioactive form. This formulation:

• Activates p53, TLR4, and histamine-related pathways
• Enhances cell-cycle modulation and immune signaling
• Synergizes with Boswellia (frankincense) for added anti-inflammatory effects

Learn more about Pathway-2™ from Ultra Botanica

For patients undergoing chemotherapy, it’s advised to avoid Pathway-2™ on the day before, day of, and day after treatment due to potential interference with cytotoxic mechanisms.

Quercetin and Cancer Final Thoughts

Quercetin is more than just a flavonoid—it’s a multi-pathway modulator with promising applications in cancer prevention, allergy relief, and oxidative stress reduction. Whether through food or enhanced supplements like Pathway-2™, integrating quercetin into your protocol may offer measurable benefits.

Quercetin References

[i] Asgharian, P., Tazekand, A.P., Hosseini, K. et al. Potential mechanisms of quercetin in cancer prevention: focus on cellular and molecular targets. Cancer Cell Int 22, 257 (2022). https://doi.org/10.1186/s12935-022-02677-w

[ii] Hashemzaei, M., Delarami Far, A., Yari, A., Heravi, R.E., Tabrizian, K., Taghdisi, S.M. ... Rezaee, R. (2017). Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports, 38, 819-828. https://doi.org/10.3892/or.2017.5766

[iii] Hashemzaei, M., Delarami Far, A., Yari, A., Heravi, R.E., Tabrizian, K., Taghdisi, S.M. ... Rezaee, R. (2017). Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports, 38, 819-828. https://doi.org/10.3892/or.2017.5766

[iv] Hashemzaei, M., Delarami Far, A., Yari, A., Heravi, R.E., Tabrizian, K., Taghdisi, S.M. ... Rezaee, R. (2017). Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports, 38, 819-828. https://doi.org/10.3892/or.2017.5766

[v] Hashemzaei, M., Delarami Far, A., Yari, A., Heravi, R.E., Tabrizian, K., Taghdisi, S.M. ... Rezaee, R. (2017). Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports, 38, 819-828. https://doi.org/10.3892/or.2017.5766

[vi] Hashemzaei, M., Delarami Far, A., Yari, A., Heravi, R.E., Tabrizian, K., Taghdisi, S.M. ... Rezaee, R. (2017). Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports, 38, 819-828. https://doi.org/10.3892/or.2017.5766

[vii] Hashemzaei, M., Delarami Far, A., Yari, A., Heravi, R.E., Tabrizian, K., Taghdisi, S.M. ... Rezaee, R. (2017). Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports, 38, 819-828. https://doi.org/10.3892/or.2017.5766

[viii] Hashemzaei, M., Delarami Far, A., Yari, A., Heravi, R.E., Tabrizian, K., Taghdisi, S.M. ... Rezaee, R. (2017). Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports, 38, 819-828. https://doi.org/10.3892/or.2017.5766

[ix] Hashemzaei, M., Delarami Far, A., Yari, A., Heravi, R.E., Tabrizian, K., Taghdisi, S.M. ... Rezaee, R. (2017). Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports, 38, 819-828. https://doi.org/10.3892/or.2017.5766

[x] Hashemzaei, M., Delarami Far, A., Yari, A., Heravi, R.E., Tabrizian, K., Taghdisi, S.M. ... Rezaee, R. (2017). Anticancer and apoptosis‑inducing effects of quercetin in vitro and in vivo. Oncology Reports, 38, 819-828. https://doi.org/10.3892/or.2017.5766

[xi] Xie, X., & Wei, Y. (2025). A review on anti-cancer properties of quercetin in gastric cancer. Frontiers in Pharmacology, 16, 1563229. https://doi.org/10.3389/fphar.2025.1563229

[xii] Asgharian, P., Tazekand, A.P., Hosseini, K. et al. Potential mechanisms of quercetin in cancer prevention: focus on cellular and molecular targets. Cancer Cell Int 22, 257 (2022). https://doi.org/10.1186/s12935-022-02677-w

[xiii] Aghababaei, F., & Hadidi, M. (2023). Recent Advances in Potential Health Benefits of Quercetin. Pharmaceuticals, 16(7), 1020. https://doi.org/10.3390/ph16071020

[xiv] Tsai, F., Chen, W., Chen, C., Shen, K., Lu, Y., Yang, Y., Chen, H., & Yeh, L. (2021). Regulatory Effects of Quercetin on M1/M2 Macrophage Polarization and Oxidative/Antioxidative Balance. Nutrients, 14(1), 67. https://doi.org/10.3390/nu14010067

[xv] Zielińska, D., Starowicz, M., Wronkowska, M., & Zieliński, H. (2025). Multifaceted Biological Activity of Rutin, Quercetin, and Quercetin’s Glucosides. Molecules, 30(12), 2555. https://doi.org/10.3390/molecules30122555

[xvi] Di Petrillo A, Orrù G, Fais A, Fantini MC. Quercetin and its derivates as antiviral potentials: A comprehensive review. Phytotherapy Research. 2021;36(1):266-278. doi: https://doi.org/10.1002/ptr.7309

[xvii] Roy, A.V., Chan, M., Banadyga, L. et al. Quercetin inhibits SARS-CoV-2 infection and prevents syncytium formation by cells co-expressing the viral spike protein and human ACE2. Virol J 21, 29 (2024). https://doi.org/10.1186/s12985-024-02299-w

[xviii] Huh, S., Lee, S., Choi, S. J., Wu, Z., Cho, H., Kim, L., Shin, Y. S., Kang, B. W., Kim, J. G., Liu, K., Cho, H., & Kang, H. (2019). Quercetin Synergistically Inhibit EBV-Associated Gastric Carcinoma with Ganoderma lucidum Extracts. Molecules, 24(21), 3834. https://doi.org/10.3390/molecules24213834

[xix] Petrillo, A. D., Orrù, G., Fais, A., & Fantini, M. C. (2022). Quercetin and its derivates as antiviral potentials: A comprehensive review. Phytotherapy Research, 36(1), 266-278. https://doi.org/10.1002/ptr.7309

[xx] Zhong, D., Liu, M., Cao, Y., Zhu, Y., Bian, S., Zhou, J., Wu, F., Ryu, C., Zhou, L., & Ye, D. (2015). Discovery of Metal Ions Chelator Quercetin Derivatives with Potent Anti-HCV Activities. Molecules, 20(4), 6978. https://doi.org/10.3390/molecules20046978

[xxi] Šudomová, M., & Hassan, S. T. (2023). Flavonoids with Anti-Herpes Simplex Virus Properties: Deciphering Their Mechanisms in Disrupting the Viral Life Cycle. Viruses, 15(12), 2340. https://doi.org/10.3390/v15122340

[xxii] Pasetto, S., Pardi, V., & Murata, R. M. (2014). Anti-HIV-1 Activity of Flavonoid Myricetin on HIV-1 Infection in a Dual-Chamber In Vitro Model. PLoS ONE, 9(12), e115323. https://doi.org/10.1371/journal.pone.0115323