Salted fish and cured food are increasingly linked to NPC

Anthony Chan Tak-cheung, chairman of the Department of Clinical Oncology, Chinese University of Hong Kong

Nasopharyngeal carcinoma (NPC) is more prevalent in Southern China. How much more common is it in Hong Kong compared with other parts of the world? Nasopharyngeal cancer is by far more prevalent in Southern China (which includes Hong Kong), particularly in the regions of Guangzhou and Guangxi. Compared with the rest of the world, the number of incidents in Southern China exceeds that of other regions by 100 times.

Are there definitive reasons why? Yes, the circumstances that lead to nasopharyngeal cancer are well studied. The cancer generally occurs due to a combination of genetics, diet and the Epstein-Barr virus (EBV), a common herpes virus that causes infectious mononucleosis. There are multiple types of genetic mutations that predispose Southern Chinese people to the cancer, and they consequently pass it on to their children. Many incidents of NPC have also been observed in fishing populations, or in communities that spend most of their time off the land, likely due to a diet heavy on salted fish and other preserved food. EBV, one of the most common viruses in human beings, plays an essential role in NPC, and it is rare for the cancer to develop in an individual not carrying the virus.

Consumption of cured food is said to play a role. What's your opinion on that? The consumption of cured food does play a role in the development of nasopharyngeal cancer. However, an unhealthy diet alone does not directly cause NPC. The carcinogens in the cured food, combined with EBV and any genetic predisposition, all work together to create an environment conducive to the cancer.

Childhood eating habits have also been seen as a factor in some countries. Have there been studies done in Hong Kong to back that up? The occurrence rate of NPC is generally higher in populations that have consistently, from a young age, consumed large amounts of salted or preserved food. Studies were conducted decades ago concluding that mice sustained on a diet heavy in preservatives consequently developed the cancer. These results have long been accepted and published in textbooks, and efforts are now being concentrated on enabling an earlier diagnosis and improving the current treatments.

What sort of work is being done right now in terms of medical treatment? Due to the significant role of the Epstein-Barr virus in NPC, there is considerable interest in using the virus as a factor in the development of a treatment. A modified EBV vaccine that aims to clean up any remaining harmful cells after chemotherapy is being manufactured in Britain and will later be tested in Hong Kong.