The question gets asked all the time in green circles, though not always with the recommended dose of skepticism: Can marijuana cure cancer?

As far as science is concerned, the definitive answer is a resounding “Who knows?” But signs of hope are popping up everywhere, and a new one came to light in late October.

A researcher in the United Kingdom has discovered that certain cannabis compounds can kill cancer cells in people who suffer from leukemia. These findings could be significant for patients with the disease, a form of cancer estimated to kill 24,000 people yearly in the United States.

Liu, an oncologist at St. George’s medical school at the University of London, separated six non-psychoactive cannabinoids from marijuana and tested them against leukemia cells, alone and in combination. These chemicals include cannabidiol (CBD), cannabidiolic acid (CBDA), cannabigerol (CBG), and cannabigerolic acid (CBGVA). Liu didn’t test THC, the psychoactive chemical that gets pot users high.

Liu told U.S. News & World Report the cannabinoids showed “potent anti-cancer activity” and can “target and switch off” the chemical pathways that make it possible for cancers to grow.

“There’s quite a lot of cancers that should respond quite nicely to these cannabis agents,” Liu said. “If you talk about a drug company that spent billions of pounds trying to develop these new drugs that target these pathways, cannabis does exactly the same thing – or certain elements of cannabis compounds do exactly the same thing – so you have something that is naturally produced which impacts the same pathways that these fantastic drugs that cost billions also work on.”

Liu said he was hopeful his findings could lead to treatments within a year to 18 months, after further research.

But he said it isn’t clear whether the cannabinoids would have the same effect on other cancer cells. Also, he used pure cannabis extracts, and said there’s no research to suggest smoking pot would have similar outcomes.

“When we talk about smoking marijuana versus marijuana in its purest form, it’s very difficult to say,” Liu said. “I get asked that a lot. I wouldn’t say, ‘Smoke marijuana to fight leukemia,’ only because we don’t know how these different chemicals react with each other inside the patient who smokes it.”

Previous studies have also found hopeful signs that marijuana could help treat cancer. Last year, scientists at the California Pacific Medical Center in San Francisco discovered that CBD can stop metastasis in many kinds of cancer. Another study in 2012, funded by the National Cancer Institute, found that cannabinoids may slow the growth of breast cancer.