Fenbendazole and Cancer: What Does the Latest Research Say?

Abstract

Cancer continues to pose a significant global health burden, particularly with the rise of aggressive and treatment-resistant malignancies such as triple-negative breast cancer, pancreatic adenocarcinoma, and glioblastoma. In response to the limitations of current therapies, there is growing interest in the repurposing of antiparasitic agents—specifically fenbendazole—for oncological applications. This review synthesizes recent preclinical and emerging clinical evidence on the anticancer mechanisms and therapeutic potential of this drug. Fenbendazole, a benzimidazole compound, demonstrates anticancer activity through microtubule destabilization, cell cycle arrest, and inhibition of glucose metabolism, though its clinical application is challenged by poor solubility and bioavailability. Despite promising laboratory and anecdotal clinical results, robust randomized controlled trials are lacking, and regulatory approval for cancer indications remains limited. The review highlights the need for further clinical research, pharmacokinetic optimization, and standardized protocols to fully realize the potential of this affordable, multi-targeted agent as adjunctive cancer therapies, particularly in resource-constrained settings.

Keywords: Cancer, Drug Repurposing, Fenbendazole, Antiparasitic Agents, Oncology, Drug Resistance, Adjunctive Therapy, Pharmacokinetics, Cancer Stem Cells, Affordable Cancer Treatments.

Introduction

Cancer remains a leading cause of morbidity and mortality worldwide, with an increasing incidence of aggressive and treatment-resistant tumors such as triple-negative breast cancer (TNBC), pancreatic adenocarcinoma, and glioblastoma. Despite significant advances in targeted therapies and immunotherapies, many patients continue to face limited effective options, highlighting an urgent need for novel, affordable, and accessible treatment strategies. 

The high cost of oncology drugs-exceeding $150 billion globally in 2022-and the slow pace of new drug approvals further complicate timely patient access to effective therapies. In this context, drug repurposing-the strategy of identifying new therapeutic uses for existing drugs-has emerged as a promising approach to accelerate cancer treatment development while reducing costs and safety risks.

Among repurposed candidates, antiparasitic drugs such as fenbendazole, mebendazole, and ivermectin have attracted considerable attention due to their demonstrated anticancer activities across multiple preclinical models and emerging clinical case reports. These agents, originally developed to treat helminth infections, exert multifaceted effects on cancer cells, including disruption of microtubule dynamics, interference with metabolic pathways, and modulation of oncogenic signaling.

Fenbendazole, traditionally an anthelmintic drug used to treat parasitic infections in animals, has recently gained attention for its potential anticancer properties. While not yet approved for cancer treatment in humans, emerging preclinical studies reveal promising mechanisms by which fenbendazole may inhibit tumor growth and overcome drug resistance.

Fenbendazole has shown potent anticancer effects by destabilizing microtubules, inducing G2/M cell cycle arrest, and impairing glucose metabolism through inhibition of glucose transporters (GLUT1/4) and hexokinase activity. These actions lead to reduced glycolysis and lactate production, effectively starving cancer cells and overcoming drug resistance, particularly in 5-fluorouracil-resistant colorectal cancer models (Bai et al., 2009; Oral Fenbendazole for Cancer Therapy, 2024; Anti-cancer effects of fenbendazole on 5-fluorouracil-resistant cells, 2022). However, fenbendazole’s poor water solubility and limited oral bioavailability present challenges for achieving therapeutic systemic levels, necessitating formulation improvements and pharmacokinetic optimization.

Despite encouraging preclinical and anecdotal clinical evidence, fenbendazole remains largely experimental in oncology, with limited randomized controlled trials* and regulatory approval for cancer indications. Variability in dosing protocols, access issues, and concerns about off-label use underscore the need for rigorous clinical evaluation. Nonetheless, the low cost, oral administration, and multi-targeted anticancer properties position fenbendazole as an attractive candidate for adjunctive cancer therapy, especially in resource-limited settings.

This review aims to synthesize current knowledge on the anticancer mechanisms, clinical case reports, pharmacokinetics, and safety profiles of fenbendazole. We discuss the potential roles in overcoming drug resistance, improving patient outcomes, and informing future clinical trials that could integrate these repurposed agents into standard oncology practice.

*Note: The Randomised Controlled Trial (RCT) method for hard evidence is a very expensive and impractical model when it comes to something as complicated as cancer. Most drugs are designed to affect one part of cancer and not the other parts of cancer or even the root causes of cancer. To understand more of this concept, check out 'hallmarks of cancer'. The randomized placebo-controlled trial (RCT)* is widely regarded as the gold standard for generating high-quality evidence in medicine. However, when it comes to cancer, the RCT model is often prohibitively expensive, time-consuming, and sometimes impractical. See "Randomised controlled trials (RCTs), are often costly, slow, and logistically challenging - ChatGPT".

Promising Anti-Cancer Mechanisms of Fenbendazole

Research shows fenbendazole exerts anticancer effects primarily by disrupting cancer cell metabolism and division:

• Inhibition of Glycolysis and Glucose Uptake: Cancer cells rely heavily on glycolysis (the Warburg effect) for energy, even in oxygen-rich environments. Fenbendazole blocks glucose transporters such as GLUT1 and inhibits hexokinase II (HKII), key proteins in glucose metabolism. This starves cancer cells of energy, reducing lactate production that otherwise promotes tumor progression and drug resistance (1, 4).
• Activation of Tumor Suppressor p53: Fenbendazole enhances the activity of p53, a protein that regulates cell cycle arrest and apoptosis. This activation leads to mitochondrial injury and triggers programmed cancer cell death via caspase pathways (1, 4).
• Microtubule Destabilization and Cell Cycle Arrest: Fenbendazole disrupts microtubule polymerization, essential for cell division, causing arrest in the G2/M phase of the cell cycle. This prevents cancer cells from proliferating and induces apoptosis, as demonstrated in colorectal cancer cells and patient-derived tumor organoids (2, 3, 4).
• Multi-Modal Anticancer Effects: Beyond glycolysis inhibition and cell cycle arrest, fenbendazole induces necrosis, autophagy, and ferroptosis in cancer cells, attacking tumors through multiple pathways and potentially reducing the likelihood of resistance development (1, 4).

Evidence from Preclinical Studies

• In Vitro and Animal Models: Numerous laboratory studies have demonstrated fenbendazole’s ability to inhibit tumor growth in various cancer types, including colorectal, cervical, pancreatic, and drug-resistant cancers. Oral fenbendazole reduced tumor size and grade in mouse models, supporting its potential efficacy12367.

• Overcoming Drug Resistance: Fenbendazole showed effectiveness against cancer cells resistant to common chemotherapies like 5-fluorouracil (5-FU), paclitaxel, and docetaxel, making it a candidate for combination therapies or treatment of refractory cancers13.

Challenges and Considerations

Despite encouraging results, fenbendazole faces significant hurdles before clinical adoption:

• Poor Water Solubility and Bioavailability: Fenbendazole’s low solubility limits its absorption and systemic availability, reducing therapeutic levels in tumors. Research is ongoing to improve drug formulations, such as nanoparticle delivery systems, to enhance efficacy13.

• Lack of Clinical Trials: To date, there are no large-scale, peer-reviewed clinical trials validating fenbendazole’s safety and effectiveness as a cancer treatment in humans. Most evidence remains preclinical or anecdotal148.

• Safety Profile: Fenbendazole is generally considered safe in animals with minimal toxicity. However, its effects in humans, especially at doses required for anticancer activity, need thorough evaluation1.

Public Interest and Anecdotal Reports

The story of Joe Tippens, who reportedly used fenbendazole alongside immunotherapy for lung cancer, has popularized fenbendazole in patient communities. While his case is inspiring, medical experts caution that his remission is more likely attributable to FDA-approved therapies rather than fenbendazole alone4.

Fenbendazole for Neuroendocrine Cancer

Stage 4 Rectal Cancer patient (small cell Neuroendocrine) with metastases to the liver and bones (April 2025)

Dr William Makis shared on X/Twitter:

IVERMECTIN and FENBENDAZOLE Testimonial - Stage 4 Rectal Cancer patient (small cell Neuroendocrine) with metastases to the liver and bones has a dramatic response to therapy!

"My mother has Stage 4 Colorectal Cancer - spread to liver and bones. Please help us! Dear Dr.Makis, a friend from work told me about your protocol using Fenbendazole and Ivermectin. My mother is in the hospital and I'm afraid for her life".

Let's say I made a few small suggestions. 

And not even 3 months later:

"We received some incredible news from her oncologist. The doctor said the scans were AMAZING! He is very, very happy. The tumor has shrunk more than half and changed density for the better. The liver and all the other places it was going are practically undetectable"

And of course my favorite part:  "We are overwhelmed with gratitude for this progress, especially after being told this cancer was likely terminal. Your protocol has given us both hope and healing, and we thank God for leading us to you." These beautiful emails fill my heart with joy.

Small Cell Cancer like this is much more aggressive than its Colorectal adenocarcinoma counterpart and chemo response isn't all that great.

Unless you add repurposed drugs.

• Ivermectin 80mg/day
• Fenbendazole 888mg/day

Initially, she had started with Ivermectin 24mg and Fenbendazole 444mg. I use higher doses and have higher rates of success than anyone else! 

Read More: Fenbendazole and Ivermectin for Colorectal Cancer (22 cases)

Conclusion and Future Directions

Fenbendazole represents a compelling example of drug repurposing in oncology, with multiple studies highlighting its ability to target cancer metabolism, induce apoptosis, and overcome drug resistance. However, the transition from laboratory findings to clinical practice requires:

• Rigorous clinical trials to establish safety, dosing, and efficacy in humans.
• Development of improved formulations to enhance bioavailability.
• Exploration of combination therapies to maximize anticancer effects while minimizing toxicity.

Given its affordability, oral administration, and multi-targeted mechanisms, fenbendazole could become a valuable adjunct in cancer treatment pending further research. Until then, patients should consult healthcare professionals and avoid self-medicating with fenbendazole outside clinical settings.

References:

1 Oral Fenbendazole for Cancer Therapy in Humans and Animals, Int J Oncol, 2024

2 Fenbendazole induces cell cycle arrest in colorectal cancer cells, AACR 2022

3 Anti-cancer effect of fenbendazole-incorporated nanoparticles, J Gynecol Oncol, 2023

4 Fenbendazole for Cancer – An In Depth Look For 2025, Trinova Health

6 Fenbendazole Exhibits Antitumor Activity Against Cervical Cancer, MDPI, 2025

7 Fenbendazole for Pancreatic Cancer: What Research Shows, Healthline

8 Separating fact from fiction: repurposed drugs in cancer treatment, Anticancer Fund