Many cancer survivors live with the worry that their cancer might come back. This "recurrence" occurs when cancer cells hide somewhere in the body - like in the bone marrow - and start growing again, sometimes years later. Scientists have been trying to understand how to stop these cells from reactivating and causing cancer to spread.
Authors
- Ahmed Elbediwy
Senior Lecturer in Cancer Biology & Clinical Biochemistry, Kingston University
- Nadine Wehida
Senior Lecturer in Genetics and Molecular Biology, Kingston University
Now, researchers are finding promising results by testing old malaria drugs as a way to prevent breast cancer from returning. This approach is called " drug repurposing ": taking medicines that already exist (even ones no longer on the market) and testing whether they can treat different diseases.
Recent studies have identified two important ways these drugs might work to treat cancer. First, they target a process called autophagy : how cells clean up and recycle their own waste. In tumours, this recycling process can help cancer cells survive when they're under stress, which means they can come back after treatment.
Second, the drugs affect genes that control cell growth . These genes, including one called mTOR, can help cancer develop from just a few damaged cells .
Together, these processes help hidden cancer cells stay viable and avoid being found by the immune system by adapting to a hostile environment . Scientists found that anti-malarial drugs - chloroquine and hydroxychloroquine - reduced the number of hidden cancer cells in both lab dishes and people .
When mice were given chloroquine, they had fewer of these hidden cancer cells and lived longer than untreated mice. These promising results encouraged scientists to start small human trials with hydroxychloroquine, a safer version of chloroquine .
The early human results look promising. In a small trial on 53 patients with minimal residual disease after standard breast cancer treatment, 92% of those who took hydroxychloroquine alone remained cancer-free after three years, compared to 93% using the targeted breast cancer therapy everolimus. A combination of both drugs showed 100% of patients remaining cancer-free at three years, with only two relapses occurring by the seven-year mark.
But there are some important limits to this study. It was a small, early trial and only included patients without active cancer. The results need confirmation in much larger, randomised controlled trials - the gold standard for testing drugs in humans - before these treatments can be considered standard care. There are still questions about the right doses, potential long-term side-effects, and which patients would benefit most.
Other drugs being explored
Several other drug classes have also shown promise in cancer research , though most are still in early testing stages.
Anti-inflammatory agents have been investigated based on the theory that they might possess anti-cancer activity, given that inflammation is a hallmark of cancer. Celecoxib, an anti-inflammatory used for arthritis, has shown some promise in blocking certain enzymes involved in tumour cell growth , though it's still being investigated.
Antibiotics , including doxycycline - commonly used to treat bacterial pneumonia and sexually transmitted infections - have been found in lab studies to slow cancer cell growth by affecting how cancer cells use energy.
Antipsychotics have also shown anti-cancer effects in early research. Thioridazine , when combined with cancer therapy in lab studies, can destroy cancer stem cells - those cells that encourage cancer to return.
Blood pressure drugs have been found to make cancer cells more responsive to chemotherapy in some studies.
And, sildenafil (better known by its brand name Viagra) is being investigated for its potential in helping slow down or prevent the growth of stomach cancer , though the research is in early stages.
Drug repurposing has real advantages. Because these drugs already have prove safety records, they could potentially be used in clinics faster and at lower cost. But the journey from promising lab results to actual treatments is long and uncertain.
Many drugs that show encouraging results in lab or animal studies fail to work when tested in humans. Even when early human trials show promise, larger studies may reveal limitations, unexpected side-effects, or that benefits only apply to specific patient subgroups.
Research continues, with scientists testing repurposed drugs at every stage of cancer care. While drug repurposing is a valuable approach that could open up new treatment options and provide a more sustainable way to develop medicines, it's crucial to keep expectations realistic.
Every new idea still needs careful testing, and patients should always talk to their doctors before trying any unproven treatments.
The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
