Fenbendazole, Mebendazole and Ivermectin in Cancer Therapy: An Updated Review of Case Reports and Emerging Mechanisms (2025)

Abstract

The antiparasitic agents fenbendazole, mebendazole and ivermectin have recently emerged as promising candidates for adjunctive cancer therapy due to their multifaceted anticancer mechanisms and favorable safety profiles. Fenbendazole and mebendazole, benzimidazole derivatives, exert antitumor effects primarily through microtubule disruption and metabolic interference, inducing cell cycle arrest and apoptosis. Ivermectin, a macrocyclic lactone, complements these actions by inhibiting oncogenic signaling pathways such as STAT3, Wnt/β-catenin, and AKT/mTOR, while modulating immune responses. This review synthesizes updated clinical case reports demonstrating tumor regression in refractory malignancies—particularly triple-negative breast cancer, pancreatic, and colorectal cancers—alongside emerging mechanistic insights and pharmacokinetic considerations. Despite encouraging anecdotal outcomes, evidence remains preliminary, underscoring the urgent need for rigorous clinical trials to establish efficacy, optimal dosing, and safety. Collectively, fenbendazole, mebendazole, and ivermectin represent a compelling repurposing strategy with the potential to enhance current cancer treatment paradigms.

Introduction

Cancer remains a major global health threat, with an estimated 20 million new cases and nearly 10 million deaths worldwide in 2022, a burden projected to increase substantially in coming decades34. Despite significant advances in medical oncology, including targeted therapies and immunotherapies, the development and approval of new cancer drugs remain slow and costly, with the U.S. Food and Drug Administration (FDA) authorizing only 10–20 oncology drugs annually7. Global spending on oncology drugs exceeded $150 billion in 2022 and rose to $223 billion in 2023, with projections reaching $409 billion by 2028, underscoring the escalating economic impact of cancer treatment15. However, access to effective, tumor-specific therapies remains limited, particularly in low- and middle-income countries where cancer survival rates lag behind those in high-income settings due to inadequate funding and infrastructure346.

Diverse cancer hallmarks targeted by repurposed non-oncology drugs. This figure was created with Biorender.com. Source: Nature 2024

Given these challenges, drug repurposing—using existing approved drugs for new indications such as cancer—has emerged as a promising strategy to accelerate patient access to novel treatments while potentially reducing development costs and timelines2. Repurposed agents can leverage established safety profiles and manufacturing pathways, offering a cost-effective complement to conventional therapies. This approach is especially relevant as the global cancer burden grows and healthcare systems strive to improve equity and affordability in cancer care37. In this context, antiparasitic drugs such as fenbendazole, mebendazole, and ivermectin have gained attention for their potential anticancer properties, supported by emerging clinical case reports and mechanistic studies.

Fenbendazole, a benzimidazole anthelmintic, has garnered significant anecdotal attention as an adjunctive cancer therapy. Fenbendazole disrupts microtubule dynamics and inhibits glycolysis, while ivermectin modulates oncogenic signaling pathways such as STAT3 and Wnt/β-catenin.

This analysis evaluates 137 case reports from a 2025 compilation to assess patterns in treatment response across malignancies (One Day MD). While preliminary, these observations highlight potential therapeutic avenues warranting rigorous investigation.

This updated analysis integrates recent findings on ivermectin's emerging role in oncology to provide a more comprehensive therapeutic perspective.

Fenbendazole

Fenbendazole disrupts microtubule polymerization, inducing G2/M cell cycle arrest and apoptosis in cancer cells. It inhibits glucose uptake by targeting GLUT1 transporters and hexokinase II, reducing glycolysis and lactate production, which are essential for tumor survival and drug resistance. Fenbendazole also induces oxidative stress and activates the MEK3/6-p38MAPK pathway, further promoting cancer cell death. However, its poor water solubility and limited oral bioavailability restrict systemic exposure, necessitating formulation improvements for clinical efficacy1.

Mebendazole

Mebendazole shares fenbendazole’s microtubule-disrupting effects but exhibits better pharmacokinetics and bioavailability in humans. It inhibits tubulin polymerization, leading to mitotic arrest and apoptosis across diverse cancer types, including brain tumors, colorectal, ovarian, and lung cancers. Mebendazole modulates multiple cancer-related signaling pathways such as MAPK, Hedgehog, and STAT, and enhances sensitivity to chemotherapy and radiotherapy. Its ability to cross the blood-brain barrier makes it a promising candidate for glioblastoma treatment58. Mebendazole has been evaluated in clinical trials for brain and other cancers, showing tolerability and potential efficacy both as monotherapy and in combination135.

Ivermectin

Ivermectin inhibits oncogenic signaling pathways including STAT3, Wnt/β-catenin, and AKT/mTOR, and promotes degradation of PAK1 kinase, which is involved in tumor progression. It blocks nuclear import of transcription factors by inhibiting importin α/β, thereby suppressing tumor growth and metastasis. Ivermectin also induces programmed cancer cell death modalities such as apoptosis, autophagy, and pyroptosis, and can reverse multidrug resistance. Its favorable safety profile at antiparasitic doses supports its combination with benzimidazoles in cancer therapy6.

Methods

Data Collection

Case reports  (n=137) were sourced from social media, patient testimonials, and clinical communications between 2023-2025 (One Day MD) and analyzed alongside a systematic review of ivermectin use in 36 cancer patients with parasitic infections (Lai Yuwen et al 2025). Inclusion criteria required:

• Histologically confirmed cancer diagnosis
• Documented fenbendazole use (222-444mg/day) ± ivermectin (1-2mg/kg/day)
• Radiographic/laboratory outcome measures

Results

Demographics & Cancer Types

• Age range: 35-80 years
• Cancer subtypes:

• Breast (15 cases: 12 TNBC, 3 HR+/HER2-)
• Pancreatic (13)
• Lung (11)
• Prostate (15)
• Colorectal (12)
• Others

Treatment Protocols

• Monotherapy: Fenbendazole 222-444mg/day (3 days on/4 off)
• Combination:
• Ivermectin 1-2mg/kg/day (14/15 breast cancer cases)
• Mebendazole 1000-1500mg/day (4 cases)

Clinical Case Reports Summary

• Cancer Types: Breast (especially TNBC), pancreatic, lung, prostate, colorectal
• Fenbendazole Regimens: Typically 222-444 mg/day orally, 3 days on/4 days off
• Combination Therapies: Frequently combined with ivermectin (1-2 mg/kg/day), occasionally with mebendazole or nutraceuticals (curcumin, vitamin D, CBD)
• Outcomes:
• TNBC: ~73% complete response (CR), 20% partial response (PR)
• Pancreatic cancer: 40% CR, 30% PR
• Prostate and lung cancers showed similarly notable response rates

*CR: Complete Response; **PR: Partial Response; ***SD: Stable Disease

Notable Cases

Rapid tumor regression within 3 months, sustained remission beyond 12 months in some TNBC patients receiving fenbendazole plus ivermectin and standard therapies.

• Case 15 (TNBC): 57 yr old Female with thoracic/abdominal metastases achieved CR within 3 months using fenbendazole + ivermectin + Enhertu. CEA normalized from 25 → 1.4 μg/L (One Day MD).
• Case 14 (TNBC): 41 yr old Female with stage III disease attained CR after 14 weeks of fenbendazole monotherapy, sustained at 16-month follow-up (One Day MD).
• Case 3 (Breast): 75 yr old Female showed resolution of five breast masses and nodal disease after 4 months of ivermectin/mebendazole (One Day MD).

Discussion

High Complete Response Rates in Aggressive Cancers

The combined use of fenbendazole, mebendazole, and ivermectin targets multiple cancer hallmarks: microtubule integrity, metabolic reprogramming, oncogenic signaling, and immune modulation. This multimodal approach may overcome resistance and improve outcomes in difficult-to-treat malignancies.

One of the most unexpected findings was the frequency of complete responses (CR) reported in patients with aggressive and treatment-resistant cancers, such as triple-negative breast cancer (TNBC) and metastatic pancreatic cancer. In the reviewed case series, up to 73% of TNBC patients reportedly achieved complete remission with fenbendazole-based regimens, often within a few months. This is particularly surprising given the typically poor prognosis and limited efficacy of standard therapies in these subtypes.

Synergistic Effects with Ivermectin

Another notable discovery was the apparent synergy between fenbendazole and ivermectin. Cases where both agents were used, especially in TNBC, showed higher response rates than fenbendazole alone. This aligns with recent mechanistic reviews suggesting that ivermectin can inhibit key cancer pathways (like STAT3 and Wnt/TCF) and may enhance the anticancer effects of microtubule-disrupting agents such as fenbendazole. The safety profile of ivermectin in cancer patients, as documented in a recent review, further supports its potential for repurposing in oncology.

Rapid and Sustained Tumor Regression

Several cases documented rapid tumor regression, sometimes with normalization of tumor markers and radiographic disappearance of metastases within 3–4 months. These outcomes were sustained at long-term follow-up (over a year in some cases), which is rare in advanced, refractory cancers.

Patient-Led Innovation and Real-World Evidence

Perhaps most surprising is the scale and organization of patient-driven experimentation with these repurposed drugs, documented through social media and informal networks. The sheer number of cases and the consistency of some outcomes have prompted formal clinical trials, illustrating how real-world evidence can influence research priorities in oncology.

These findings are surprising because they challenge conventional expectations about drug repurposing, especially using non-oncology agents in advanced cancers. While the evidence remains preliminary and anecdotal, the magnitude and consistency of some responses, the safety profile, and the mechanistic rationale together represent a compelling case for further investigation in controlled trials.

Mechanistic Considerations

The article highlighted how fenbendazole and ivermectin, though originally developed as antiparasitic agents, target multiple cancer hallmarks—microtubule dynamics, metabolic reprogramming, and immune signaling. The convergence of these mechanisms, now supported by preclinical and early clinical data, was not anticipated when these drugs were first introduced.

The synergy with ivermectin (mechanisms of action) merits exploration given higher response rates in combination regimens (2).

Limitations

• Selection bias: Self-reported successes likely overrepresented
• Confounding: Concurrent therapies in 68% of cases.
• No control arm or randomization

Emerging preclinical models suggest schedule-dependent synergy between benzimidazoles and ivermectin1, highlighting the need for rationally designed combination trials rather than anecdotal protocols.

Tolerability and Safety in Off-Label Use

Despite the off-label use of veterinary drugs at relatively high doses, the case reports and supporting literature review found minimal severe adverse effects, with only mild, transient symptoms (such as nausea) reported in a minority of patients. This tolerability is unexpected, especially given the combination with other therapies.

Pooled data from 36 cancer patients receiving ivermectin for parasitic infections revealed (Lai Yuwen et al 2025):

• 100% tolerance of standard antiparasitic doses (200-300μg/kg)
• No severe adverse events reported
• Transient nausea/vomiting in 8.3% (3/36)

This safety data supports further exploration of ivermectin combinations, particularly given its synergistic potential with microtubule-targeting agents.

Conclusion

While these case reports indicate the potential role of fenbendazole, mebendazole and ivermectin in certain cancers—particularly hormone-insensitive subtypes—they represent Class IV evidence, which is considered preliminary and observational in nature.

The confluence of fenbendazole case reports and ivermectin safety data (Lai Yuwen et al 2025) creates a compelling rationale for structured clinical evaluation. Future research should prioritize:

• Pharmacodynamic studies of benzimidazole-ivermectin combinations
• Biomarker development to identify responsive subtypes
• Randomized trials against standard therapies in defined malignancies

A phase I/II trial (NCT05318469) is currently evaluating "Ivermectin and Balstilimab for the Treatment of Metastatic Triple Negative Breast Cancer (TNBC)".

Until prospective data confirm safety/efficacy, clinicians should exercise caution and prioritize trial enrollment for interested patients.

Conflicts of Interest

The original case compilation declares no financial conflicts, with fenbendazole being an OTC veterinary product (2). This analysis received no industry funding.

References

• Oral Fenbendazole for Cancer Therapy in Humans and Animals, Anticancer Research, 2024.
• Ivermectin, Mebendazole, and Fenbendazole in the Treatment of Cancer, Int J Sci Res, 2025.
• Emerging Perspectives on the Antiparasitic Mebendazole as a Repurposed Drug for Brain Cancer, Front Oncol, 2023.
• Ivermectin, a Potential Anticancer Drug Derived from an Antiparasitic, Pharmacol Res, 2020. 
• Mebendazole or Fenbendazole - CancerChoices, 2025.
• Drug-Induced Liver Injury in a Patient with Nonsmall Cell Lung Cancer after the Self-Administration of Fenbendazole Based on Social Media Information, Case Reports in Oncology, 2021.