A compound found in cannabis may stop breast cancer spreading throughout the body, US scientists believe.
The California Pacific Medical Center Research Institute team are hopeful that cannabidiol or CBD could be a non-toxic alternative to chemotherapy.
Unlike cannabis, CBD does not have any psychoactive properties so its use would not violate laws, Molecular Cancer Therapeutics reports.
The authors stressed that they were not suggesting patients smoke marijuana.
They added that it would be highly unlikely that effective concentrations of CBD could be reached by smoking cannabis.
Past work has shown CBD can block aggressive human brain cancers.
The latest work found CBD appeared to have a similar effect on breast cancer cells in the lab.
Maria Leadbeater of Breast Cancer Care said: "Many people experience side-effects while having chemotherapy, such as nausea and an increased risk of infection, which can take both a physical and emotional toll.
"Any drug that has fewer side-effects will, of course, be of great interest."