A form of covert treatment that sends a "scout" enzyme into a tumour to single it out for destruction has been developed, scientists say.
The treatment works by only targeting the tumour
The Institute of Cancer Research project showed the drugs delayed tumour growth in animal experiments.
The therapy works by identifying tumours and using non-toxic drugs that become active when they hit the target.
Experts said it could "greatly improve" patients' quality of life, but needed to go through human trials first.
Standard cancer treatments, such as chemotherapy, treat cancer anywhere in the body by indiscriminately attacking all cells in the region.
The treatment damages healthy cells as well as cancerous ones, which is why patients have side effects, including nausea, fatigue and hair loss.
But the stealth treatment, known as gene-directed enzyme prodrug therapy, avoids harming other cells by using a "scout" enzyme to mark a tumour for destruction by the non-toxic prodrugs, the Journal of Medicinal Chemistry reported.
Previous research into prodrugs have not been successful because the prodrugs were not able to attack the tumour sufficiently.
But this time scientists were able to get them to penetrate the cancerous cells much deeper than before.
Lead researcher Professor Caroline Springer said: "These drugs are a very promising way forward for cancer treatment.
"Although it is more complex than many types of therapies, the fact it can be so selective in treating cancer means it is worth exploring further."
Professor John Toy, medical director at Cancer Research UK, which funded the project, added: "This type of therapy should theoretically work and is showing promise.
"The benefits this therapy could offer, in terms of more comfortable treatment and reduced side effects, could greatly improve the quality of life for people living with cancer or allow larger doses to be prescribed."
But he said the real test would come during clinical trials of the drug on patients.