According to US scientists, a harmful virus that can cause devastating damage to the brains of developing fetuses could offer up a surprising new treatment for adult brain cancer.
Zika has been seen only as a global health threat - not a remedy until now.
But latest research shows the virus can selectively infect and kill hard-to-treat cancerous cells in adult brains.
Zika injections shrank aggressive tumours in fully grown mice, yet left other brain cells unscathed.
Human trials are still a way off, but experts believe Zika virus could potentially be injected into the brain at the same time as surgery to remove life-threatening tumours, the Journal of Experimental Medicine reports.
The Zika treatment appears to work on human cell samples in the lab.
There are many different types of brain cancer. Glioblastomas are the most common in adults and one of the trickiest to treat.
They are fast growing and diffuse, meaning they spread through the brain, making it difficult to see where the tumour ends and the healthy tissue begins.
Radiotherapy, chemotherapy and surgery may not be enough to remove these invasive cancers.
But the latest research, in living mice and donated human brain tissue samples, shows Zika therapy can kill cells that tend to be resistant to current treatments.
It is thought that these glioblastoma stem cells continue to grow and divide, producing new tumour cells even after aggressive medical treatment.
Different, healthy stem cells are found in abundance in baby brains, which probably explains why regular Zika can be so damaging to infants, say the researchers.
Adult brains, however, have very few stem cells. This means Zika treatment should destroy only the cancer-causing brain stem cells without causing much collateral damage.
As an extra safety precaution, the team, from Washington University School of Medicine and the University of California San Diego School of Medicine, have already begun modifying the virus to make it more tame than regular Zika.
Researcher Dr Michael Diamond said: "Once we add a few more changes, I think it's going to be impossible for the virus to overcome them and cause disease.
"It looks like there's a silver lining to Zika. This virus that targets cells that are very important for brain growth in babies, we could use that now to target growing tumours."
He hopes to begin human trials within 18 months.
Using viruses to fight cancer is not a new idea, but using Zika as the weapon of choice is.
UK scientists at the University of Cambridge are beginning similar trials with zika.
Dr Catherine Pickworth, from Cancer Research UK, said: "This promising research shows that a modified version of the Zika virus can attack brain tumour cells in the lab.
"This could one day lead to new treatments for this particularly hard to treat type of cancer."