A green tea extract may help patients with a form of leukaemia, a study says.
The tea, discovered in China nearly 5,000 years ago, has long been thought to have health benefits. But the team from the Mayo Clinic in the US found it appeared to improve the condition of four patients with chronic lymphocytic leukaemia (CLL).
Experts said the Leukaemia Research journal study was interesting but more research was needed.
CLL is a blood and bone marrow cancer which affects white blood cells and is the commonest type of leukaemia with over 3,000 new cases - mainly in the over 60s - diagnosed each year in the UK.
It is called chronic leukaemia because it progresses more slowly than acute leukaemia with some patients living for decades with the disease.
As there is no known cure, doctors have traditionally not intervened in the early stages of the disease to see how it develops, before moving on to traditional forms of cancer treatment such as chemotherapy.
But the Mayo researchers decided to try green tea after a test tube study in 2004 showed it killed leukaemia cells.
Four CLL patients being treated at the clinic took green tea extract tablets containing epigallocatechin gallate, an antioxidant thought to fight cancer cells.
Within a few months, doctors realised that three out of four patients were showing signs of the cancer regressing.
The fourth patient also showed a slight improvement, but it was not judged to be clinically relevant.
Report author Tait Shanafelt said: "Green tea has long been thought to have cancer-prevention capabilities. It is exciting that research is now demonstrating this agent may provide new hope for CLL patients.
"The experience of these individuals provides some suggestion that our previously published laboratory findings may actually translate into clinical effects for patients with this disease."
But he warned more research was needed to prove the findings on a larger scaled and whether there were any side effects.
Ken Campbell, clinical information officer at the Leukaemia Research Fund, said: "The findings are interesting, but we cannot say yet this is a new treatment for cancer.
"We need to carry out a large scale, controlled trial to see if the findings hold true."