Scientists said that a plant extract used in Chinese herbal remedies for arthritis, gout and inflammation has been directly linked to cancer and causes a surprising number of genetic mutations.
The gene signature of aristolochic acid -- derived from a vine known as birthwort -- was found in tumors from 19 upper urinary tract cancer patients from Taiwan.
Scientists have long known that the acid was a carcinogen, but the new study shows for the first time that it causes far more genetic mutations than smoking-related lung cancer or ultraviolet radiation-associated with skin cancer.
Tumors in people exposed to the herb had about 150 mutations per megabase, compared to eight in smoking-related lung cancers and 111 in UV-related melanomas, said the study in the US journal Science Translational Medicine.
Knowing more about the acid's signature will help researchers screen for the herb's involvement in cancers of other organs, experts said.
"Genome-wide sequencing has allowed us to tie aristolochic acid exposure directly to an individual getting cancer," said Kenneth Kinzler, professor of oncology in the Johns Hopkins Kimmel Cancer Center's Ludwig Center for Cancer Genetics and Therapeutics.
"The technology gives us the recognizable mutational signature to say with certainty that a specific toxin is responsible for causing a specific cancer."
The herb's cancer links led to a ban on aristolochic acid-containing products in Europe and North America in 2001 and in Asia in 2003, the researchers said.