The Fenbendazole Retraction, Explained: What Actually Changed in the Cancer Case-Report Evidence (2026)

Medically Reviewed by: Cancer Advisor Editorial Team  |  Last Updated: July 2026  |  Category: Repurposed Drugs, Cancer

In January 2026, a widely cited peer-reviewed case series on fenbendazole and cancer was retracted. Here's exactly what happened, why it was retracted, and — just as important — what the retraction does not tell us.

Quick Answer

In January 2026, the journal Case Reports in Oncology (Karger) retracted a May 2025 case series by William Makis, Ilyes Baghli, and Pierrick Martinez describing three Stage IV cancer patients (breast, prostate, melanoma) who added fenbendazole to their treatment and went into complete or near-complete remission. The retraction was issued because the lead author had an undisclosed financial conflict of interest — he offered clinical services related to fenbendazole use at the time of submission — not because an investigation found the patients' outcomes to be fabricated or incorrect. The paper can no longer be cited as validated peer-reviewed literature. But the underlying evidence tier hasn't changed: this was always an uncontrolled, three-patient case series.

Contents

1. What Happened: The Paper and the Retraction
2. Why It Was Retracted — And Why That's Different From Being Disproven
3. Where This Evidence Sat on the Evidence Pyramid (Before and After)
4. What Actually Changed vs. What Didn't
5. The Broader Case-Report Picture
6. Regulatory and Institutional Context
7. Practical Guidance If You're Considering This
8. Frequently Asked Questions
9. Ask an AI Assistant About This

1. What Happened: The Paper and the Retraction

In May 2025, Case Reports in Oncology published "Fenbendazole as an Anticancer Agent? A Case Series of Self-Administration in Three Patients," authored by William Makis, Ilyes Baghli, and Pierrick Martinez. The paper documented three patients with Stage IV disease — an 83-year-old woman with recurrent ER-positive breast cancer, a man with metastatic prostate cancer, and a patient with metastatic melanoma — who incorporated fenbendazole, an over-the-counter veterinary antiparasitic, into their care. According to the paper, two patients reached complete remission and one reached near-complete remission, with follow-up ranging from about 11 months to nearly three years at the time of publication, and no reported adverse effects attributed to fenbendazole.

Because it appeared in a peer-reviewed, PubMed-indexed journal, this case series quickly became the most-cited piece of "clinical literature" across the fenbendazole-for-cancer community — including in some of the case-series compilations on this site and its sister property.

On January 21, 2026, Karger's Editor for Case Reports in Oncology, Dr. Maurie Markman, retracted the paper. The retraction notice states that concerns were raised about an undeclared conflict of interest: at the time of submission, the lead author offered clinical services related to the subject of the study — meaning he treated patients with fenbendazole as part of his practice — and this was not disclosed in the article's conflict-of-interest statement. The journal contacted the author, found the response unsatisfactory, and concluded the omission would have affected how the work should be interpreted.

2. Why It Was Retracted — And Why That's Different From Being Disproven

This distinction matters enough to state plainly: retraction for an undisclosed conflict of interest is not the same as retraction for fabricated, falsified, or disproven data. Journals retract papers for several different reasons, and they carry very different implications:

Retraction Reason	What It Implies	Applies to the Makis Case Series?
Fabricated or falsified data	The reported results may not have happened at all	No
Methodological error invalidating conclusions	The analysis was flawed in a way that changes what the data shows	No
Undisclosed conflict of interest	The author had a stake in the outcome that readers weren't told about, which could bias case selection or framing	Yes — this is the stated reason

A conflict-of-interest retraction is a real problem — it means readers were denied information they needed to properly weigh the report, and it's fair to ask whether a treating physician who also promotes a therapy is more likely to select and frame favorable cases. But it is a procedural and disclosure failure, not a finding that the three patients' scans, biomarkers, or clinical courses were fictitious. The retraction notice does not claim the clinical data was inaccurate.

3. Where This Evidence Sat on the Evidence Pyramid (Before and After)

Using the Oxford Centre for Evidence-Based Medicine (CEBM) hierarchy — the tiering system we apply across this site — it's worth being honest about where an N=3, uncontrolled case series always sat, retraction or not:

CEBM Level	Evidence Type	Where the Makis Paper Sat
1	Systematic reviews of RCTs	—
2	Individual RCTs	—
3	Cohort / case-control studies	—
4	Case series	Here — before retraction
5	Expert opinion, anecdotal reports, non-peer-reviewed accounts	Here — after retraction, and where most other fenbendazole/ivermectin case reports (including Substack- and social-media-sourced compilations) sit regardless

In plain terms: peer review of a three-patient case series never meant fenbendazole's anticancer effect in humans was "proven." It meant the write-up passed an editorial and peer-review process for publication as a case report — the lowest rung of clinical evidence that still counts as a formal study design. Losing that peer-reviewed status is a real demotion in citability. It is not a demotion from "proven" to "unproven," because it was never more than hypothesis-generating to begin with.

4. What Actually Changed vs. What Didn't

Changed	Didn't Change
The paper's status — from citable peer-reviewed literature to a retracted article that should not be cited as validated evidence.	Whether the three patients experienced the reported clinical courses. That specific factual question was not the subject of the retraction.
Indexing — the article is now flagged as retracted in PubMed/PMC and by Karger.	The absence of a control group, randomization, or blinding — this was always true of the paper, retracted or not.
Any secondary source whose main credibility argument was "this is peer-reviewed" loses that specific argument for this paper.	Fenbendazole's regulatory status — still approved only for veterinary use, with no FDA approval for any human cancer indication.
	The volume of independently compiled anecdotal case reports elsewhere (including this site's own compilations) — these were never resting on the Makis paper's peer-review status in the first place, since they were sourced separately from public postings.

5. The Broader Case-Report Picture

This site has compiled and reviewed hundreds of publicly reported fenbendazole, ivermectin, and mebendazole cancer cases across cancer types — see, for example, our 763-case series review and our lymphoma and leukemia case series. It's worth being direct with readers about how these compilations relate to the retracted paper: they are a different and generally lower evidence tier, not a backup copy of the same evidence.

The Makis case series, whatever its flaws, went through formal peer review, defined case-reporting standards, and editorial scrutiny before publication. Most of the broader case-report compilations — including material sourced from Substack posts and social media — are self-reported, not independently verified through chart review, and carry no peer oversight at all. None of this rises to controlled-trial evidence, and professional oncology organizations have consistently cautioned patients against substituting unproven off-label agents for standard-of-care treatment without oncologist involvement. That guidance doesn't change based on this retraction — if anything, it's a useful reminder of why it exists.

There is a genuine silver lining here: interest in studying repurposed antiparasitics through proper channels appears to be growing. In 2026, Florida announced a $60 million cancer research funding initiative that named the repurposing of generic drugs, including ivermectin, as a funding priority — a sign that the path forward (registered trials, not case-report compilations) is gaining institutional traction.

6. Regulatory and Institutional Context

• Fenbendazole: Approved by the FDA only for veterinary use (deworming livestock and companion animals). It has no FDA approval for any human indication, including cancer.
• Mebendazole: Has FDA-approved human formulations for parasitic infections, but not for cancer; any cancer use is off-label.
• Ivermectin: FDA-approved for human parasitic infections; oncology use is off-label. A handful of small registered trials are testing ivermectin in combination with approved cancer therapies (for example, a Phase II trial pairing ivermectin with balstilimab in metastatic triple-negative breast cancer), which is the type of evidence that could eventually move this question beyond the case-report tier.

None of the drugs discussed in this article are approved by the FDA or EMA for cancer treatment. Off-label use of any prescription-only agent (mebendazole, ivermectin) should only be considered under the supervision of a treating oncologist; fenbendazole is not intended for human consumption under any regulatory framework.

Important: This article is for educational purposes and does not constitute medical advice. It does not recommend for or against the use of fenbendazole, ivermectin, or mebendazole in cancer care. Decisions about cancer treatment — including any off-label or adjunct therapy — should be made with a qualified oncologist who can review your full history, monitor for interactions and adverse effects, and weigh this alongside standard-of-care treatment.

7. Practical Guidance If You're Considering This

• Don't treat any single case series — retracted or not — as proof of what will happen for your specific cancer type and stage.
• If you're already using an off-label agent alongside conventional treatment, tell your oncology team. Undisclosed supplement and off-label drug use is one of the most common sources of unmonitored interactions in cancer care.
• Ask your care team about registered clinical trials combining repurposed drugs with standard therapy, rather than relying on anecdotal protocols — this is the only path that can generate evidence stronger than case reports.
• Whenever you're evaluating a source's credibility, check whether it's peer-reviewed, whether a retraction notice exists, and whether the author disclosed any financial or clinical stake in the therapy being discussed.
• If you need help finding an oncologist or integrative specialist to discuss any of this with, our Find a Doctor directory can help you locate one. (Disclosure: this is a referral partnership; we may earn a commission at no cost to you.)

8. Frequently Asked Questions

Does the retraction mean fenbendazole doesn't work for cancer?

No. The retraction addressed an undisclosed conflict of interest, not the accuracy of the reported outcomes. But the retraction also doesn't mean fenbendazole does work — a three-patient, uncontrolled case series was never able to establish that either way, regardless of its publication status.

Were the three patients' remissions fake?

The retraction notice does not claim this. The stated reason is an undeclared financial conflict of interest by the lead author, not fabricated or falsified clinical data.

Can the paper still be cited?

It's now flagged as retracted in PubMed, PMC, and by the publisher. It can be discussed and referenced as a retracted paper — including its retraction reason — but should not be cited as validated, peer-reviewed evidence supporting fenbendazole's efficacy.

Does this affect the credibility of ivermectin and mebendazole research too?

Not directly — the retraction concerns this specific paper and this specific author's disclosure. But it's a good prompt to apply the same scrutiny (peer-review status, author disclosures, retraction watch) to any single source across this drug class.

I already discussed this paper with my doctor — should I be worried?

Bring the retraction notice to your next appointment so your care team has the full picture. This is exactly the kind of update that's worth a conversation, not a reason to make any treatment change on your own.

What would actually settle whether these drugs help?

Randomized, controlled trials with adequate sample sizes — the kind now beginning to enroll for ivermectin in combination with approved therapies. Case reports, retracted or not, can generate hypotheses; they can't confirm them.

9. Ask an AI Assistant About This

Want to dig into how this applies to your own situation? Here's how to get a more personalized follow-up from a few major AI assistants — paste in your specifics (cancer type, stage, current treatment) for a more useful answer than a generic search.

Assistant	Try asking
Claude	"Search for any registered clinical trials combining [ivermectin/mebendazole] with standard treatment for [my cancer type], and summarize the eligibility criteria."
ChatGPT	"Explain the difference between a retracted paper and a disproven finding, using the January 2026 Makis fenbendazole retraction as an example."
Gemini	"What questions should I ask my oncologist before considering an off-label repurposed drug alongside my current treatment?"
Perplexity	"Find the most recent peer-reviewed (non-retracted) literature on fenbendazole's mechanism of action in cancer cells."

AI assistants can help you find and organize information, but they aren't a substitute for a treating physician who knows your full medical history.

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References

1. Makis W, Baghli I, Martinez P. Fenbendazole as an Anticancer Agent? A Case Series of Self-Administration in Three Patients. Case Rep Oncol. 2025;18:856–863. (Retracted.)
2. Retraction Statement: Paper by William Makis, Ilyes Baghli, and Pierrick Martinez. Case Rep Oncol. 2026;19(1):169.
3. OneDayMD Editorial Team. Ivermectin, Fenbendazole and Mebendazole for Cancer: Case Series of 763 Case Reports (June 2026 Update).
4. OneDayMD Editorial Team. Ivermectin and Mebendazole in Lymphoma and Leukemia: 39 Case Reports (June 2026 Update).

This article was last reviewed for accuracy in July 2026 and will be updated if further developments occur regarding this retraction or related research.