Chinese folk remedy may promote cancer.

Chinese folk remedy may promote cancer

Two families of plants commonly used as herbal remedies in mainland China may explain the high rate of nasopharyngeal cancer found in scattered regions of that country, new research suggests.

Epidemiologists have for years puzzled over the unusual geographic distribution of nasopharyngeal cancer in China. Epstein-Barr virus, which has been widely associated with the cancer, is especially common in Asian populations. But while the virus is widespread, nasopharyngeal cancer occurs most often in particular parts of China. And laboratory scientists have been unable to spur epithelial cells, which line the nasal passages, to become cancerous with the simple addition of Epstein-Barr virus.

Now researchers report in the Sept. 3 NATURE that they have transformed normal human epithelial cells into cancer cells by exposing them to Epstein-Barr virus, but that the transformation is dependent on the presence of phorbol esters, a class of chemicals found in certain tropical plants. L. David Tomei, Ronald Glaser and their colleagues at Ohio State University in Columbus drew upon previous research linking the distribution of phorbol-ester-producing plants and the occurrence of nasopharynegeal cancer in China. Their laboratory results provide some of the clearest evidence yet of the potentially important role of environmental factors as cancer promoters.

According to Glaser, the new findings don't necessarily conflict with earlier studies by researchers at the University of Southern California that linked nasopharyngeal cancer with consumption of salted, partially rotted fish--a common dietary item in parts of China (SN: 6/29/85, p.404). Both studies are compatible with current theories about the nature of carcinogenesis, he says, in which an "initiator' (such as Epstein-Barr virus) is thought to be potentiated by a "promoter,' such as a phorbol ester. "There may be multiple factors at work here, both genetic and environmental,' he says.

Unfortunately, Tomei notes, some plants that contain potent phorbol ester cancer promoters are used as traditional herbal medicinals in Asian and African cultures. "The Chinese make hot tea from these plants, and they spray the extract onto sore throats. So what you have . . . is a folk procedure that has all the elements of tumor promotion in humans: Spraying hot extracts of phorbol ester plants onto chronically inflamed tissue in an area where nearly everybody has Epstein-Barr virus.'

Hundreds of years ago, before Epstein-Barr virus became common in China, the extracts may indeed have been worthwhile, Tomei says. "But as the virus began to spread through various [ester-exposed] groups within China, it may have had a direct role in the emergence of nasopharyngeal cancer. Certainly some kind of educational process is needed to inform people that these folk remedies are potentially dangerous.'