The Growing Interest in Repurposed Drugs for Cancer Therapy: What the Research Shows
- Dr. Kimryn Rathmell
- 2 days ago
- 7 min read
Drug repurposing — also called drug repositioning or drug reprofiling — is one of the most active and exciting areas of modern oncology research. The concept is straightforward: instead of spending 10–15 years and over a billion dollars developing a brand-new cancer drug from scratch, researchers investigate whether existing medicines already approved for other conditions might also have anti-cancer properties.
This approach has already produced some of medicine's most important cancer treatments. And across laboratories worldwide, hundreds of clinical trials are currently underway testing existing medicines — including common diabetes drugs, antibiotics, antiparasitics, and anti-inflammatory medicines — for potential roles in cancer therapy.
This article is a factual overview of the science of drug repurposing in oncology — what it is, why it matters, which drugs have already been successfully repurposed for cancer, and where the current research frontier lies.
Important note:
This article is educational and does not recommend any medicine as a cancer treatment. Cancer treatment decisions must be made exclusively by qualified oncologists and healthcare teams based on your individual diagnosis.
Why Repurpose Existing Drugs?
Developing a new cancer drug from scratch typically takes 10–17 years and costs $1–3 billion, with a failure rate of over 90% in clinical trials. Many promising compounds identified in the laboratory never reach patients.
Drug repurposing offers several compelling advantages:
Established safety data:
Approved medicines have already passed rigorous safety testing in humans. Their side effect profiles, drug interactions, dosing ranges, and toxicity limits are well characterised — dramatically reducing the risk profile of early clinical trials.
Faster pathway to trials:
Because basic safety has been established, repurposed drugs can enter Phase II efficacy trials more quickly than entirely new compounds.
Lower cost:
The pharmaceutical economics of repurposing are significantly more favourable — particularly for generic medicines where no single company holds a patent and therefore has limited financial incentive to fund expensive trials. This has led to growing interest from academic research institutions, cancer charities, and government bodies in funding repurposing research independently.
Unexpected mechanisms:
Many existing medicines turn out to have biological properties that were not known when they were first developed. As our understanding of cancer biology — particularly the molecular pathways involved in tumour growth, immune evasion, and metastasis — has deepened, scientists have been able to revisit older medicines with fresh eyes.
Drugs Successfully Repurposed for Cancer: Proven Examples
Several medicines originally developed for entirely different purposes are now established, standard-of-care cancer treatments:
Thalidomide and Lenalidomide — Multiple Myeloma
Thalidomide was withdrawn from the market in the 1960s after causing severe birth defects. Decades later, researchers discovered it had profound immunomodulatory and anti-angiogenic properties — it could suppress the formation of new blood vessels that tumours require to grow. Today, thalidomide and its derivative lenalidomide are cornerstones of multiple myeloma treatment worldwide.
All-Trans Retinoic Acid (ATRA) — Acute Promyelocytic Leukaemia (APL)
A derivative of Vitamin A, ATRA was repurposed for APL — a historically fatal subtype of acute leukaemia. It induces differentiation of leukaemic cells, essentially forcing them to mature and stop proliferating. ATRA-based therapy transformed APL from one of the most lethal leukaemias into one of the most curable, with survival rates exceeding 90% in some trials.
Metformin — Active Research in Multiple Cancers
Metformin is the world's most prescribed diabetes medicine. Epidemiological studies consistently show that diabetic patients taking metformin have lower rates of certain cancers and better outcomes following cancer diagnosis than those on other diabetes treatments. Mechanistic research suggests metformin activates AMPK — an energy-sensing enzyme — which suppresses mTOR signalling pathways important in cancer cell growth. Dozens of clinical trials are currently investigating metformin as an adjunct to standard cancer therapy in breast cancer, colorectal cancer, prostate cancer, and others. It is not yet approved as a cancer treatment, but it remains one of the most actively studied repurposed drugs in oncology.
Aspirin — Colorectal Cancer Prevention
Long-term low-dose aspirin use has been associated with reduced incidence of colorectal cancer and improved outcomes after diagnosis in multiple large epidemiological studies. The mechanism appears to involve aspirin's inhibition of COX-2, a pro-inflammatory enzyme that promotes tumour growth. The US Preventive Services Task Force has examined the evidence and acknowledges the potential colorectal cancer prevention benefit of aspirin, though the benefit must be weighed against bleeding risks.
Dexamethasone and other corticosteroids — Multiple cancers
Corticosteroids were originally developed as anti-inflammatory agents but are now routinely used across oncology — in haematological malignancies, as part of chemotherapy regimens, and for managing treatment side effects. In multiple myeloma, dexamethasone alone has anti-tumour activity.
Current Research Frontiers: Drugs Under Active Investigation
The following medicines are currently the subject of active clinical and preclinical research in cancer contexts. It is important to note that being studied is fundamentally different from being proven to work — the majority of drugs investigated in cancer research do not ultimately demonstrate sufficient clinical benefit to reach approval.
Metformin (Diabetes)
As described above Metformin is the most clinically advanced repurposed drug candidate in oncology, with dozens of ongoing Phase II and III trials.
Statins (Cholesterol-lowering medicines)
Multiple epidemiological studies suggest statin users have lower incidence of certain cancers. Laboratory research shows statins can inhibit cell proliferation and induce apoptosis (programmed cell death) in cancer cell lines. Clinical trials are ongoing across multiple cancer types.
Itraconazole (Antifungal)
Originally an antifungal, itraconazole has been found to inhibit the Hedgehog signalling pathway and VEGFR2 — both implicated in tumour growth and angiogenesis. Early clinical trials in prostate, lung, and basal cell carcinoma have shown some promising signals, though larger trials are needed.
Mebendazole and Albendazole (Antiparasitics)
Benzimidazole antiparasitics — including Mebendazole and the related compound Albendazole — have attracted research interest because of their effects on tubulin polymerisation in cells. Because tubulin disruption is a known anti-cancer mechanism (used by Taxol and Vinca alkaloids), researchers have investigated whether benzimidazoles might have anti-proliferative effects in cancer cells. In vitro (cell culture) and animal model studies have demonstrated anti-proliferative activity in several cancer cell lines. However, as of current knowledge, no randomised controlled clinical trials have demonstrated clinical efficacy in cancer patients, and no regulatory body has approved benzimidazoles for cancer treatment.
Ivermectin (Antiparasitic)
Ivermectin has also been investigated in the laboratory for potential anti-cancer properties. Preclinical research has explored its effects on various signalling pathways involved in cancer cell behaviour. As with benzimidazoles, early laboratory and animal findings are of scientific interest, but human clinical trial data supporting anti-cancer efficacy is currently lacking. Ivermectin remains an approved, effective treatment for parasitic infections.
Doxycycline (Antibiotic)
Doxycycline has been studied for potential roles in cancer biology — particularly for its effects on mitochondria and its anti-angiogenic properties at higher concentrations. Some research has investigated its use as an adjunct to conventional cancer therapy. Early-phase clinical trials have reported signals in specific contexts, though further research is required to establish clinical utility.
The Gap Between Laboratory Research and Clinical Reality
One of the most important concepts for patients and the public to understand is the difference between laboratory findings and clinical proof.
When a drug shows anti-cancer activity in a cell culture experiment or an animal model, this is a hypothesis-generating finding — it suggests the drug might be worth studying further in humans. It is not evidence that the drug treats cancer in people.
The history of oncology is filled with compounds that showed spectacular results in the laboratory and in animal models but failed to demonstrate benefit — or caused unexpected harm — when tested in humans. This is not a failure of the scientific process; it is the scientific process working as intended, carefully verifying findings before they reach patients.
Drug repurposing research is genuinely exciting, scientifically rigorous, and represents a legitimate and important area of oncology investigation. Patients with cancer who are interested in clinical trials involving repurposed drugs should speak with their oncologist about whether any current trials may be relevant to their specific diagnosis.
What This Means for Patients
If you have a cancer diagnosis and have read about a repurposed drug that might be relevant to your situation:
Speak with your oncologist
they can advise on the current state of evidence and whether any clinical trials are available to you
Search ClinicalTrials.gov
the US government's registry of current clinical trials lists ongoing studies and eligibility criteria
Be cautious of anecdotal reports
individual stories of remarkable outcomes exist for many repurposed drugs; they cannot be generalised and may reflect other factors
Never replace proven treatment
repurposed drug research is complementary to, not a replacement for, evidence-based cancer therapy
The field of drug repurposing represents genuine scientific hope — not through abandoning what we know, but through building on it carefully and rigorously.
Frequently Asked Questions
What is drug repurposing in cancer treatment?
Drug repurposing is the investigation of medicines already approved for other conditions — such as diabetes drugs, antibiotics, or antiparasitics — for potential anti-cancer properties. It takes advantage of established safety data and known mechanisms to accelerate research timelines.
Which repurposed drugs are already used in cancer treatment?
Established examples include Thalidomide and Lenalidomide for multiple myeloma, All-Trans Retinoic Acid for acute promyelocytic leukaemia, and corticosteroids across multiple cancers. Aspirin is under investigation for colorectal cancer prevention. Metformin is the subject of dozens of ongoing clinical trials.
Are antiparasitic drugs like Ivermectin or Mebendazole cancer treatments?
No regulatory body has approved Ivermectin or Mebendazole as cancer treatments. Both have been studied in laboratory settings, where preclinical data has generated scientific interest. However, preclinical findings in cell cultures and animal models do not establish clinical efficacy in humans. Clinical trials are needed to answer this question rigorously.
How can I find out about clinical trials for repurposed drugs?
Visit ClinicalTrials.gov — the US government registry of clinical trials — and search by your cancer type. Your oncologist can also guide you on whether any current trials are relevant to your diagnosis.
Should I take a repurposed drug alongside my cancer treatment without telling my doctor?
No. This is strongly inadvisable. Many medicines have interactions with standard chemotherapy and other cancer treatments that could be harmful. Any medicine you are considering must be discussed with your oncologist before you start taking it.
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