Nasopharyngeal Carcinoma (NPC)
Nasopharyngeal Carcinoma (NPC) is one of the leading causes of cancer deaths among ethnic Asian groups. Chinese individuals from Southern China have the highest risk in developing NPC. Statistics have shown that males are affected much more frequently than females with a life-time risk for developing NPC of 1 in 53 men compared to 1 in 131 women. NPC has a peak incidence in the 50 to 54 age range, with an incidence rate that starts to climb steadily to this point after 15-20 years of age. The annual mortality, or death rate, for this cancer exceeds 73,000 annually which is a tragic statistic because NPC can be cured when detected early.
Where is NPC endemic?
NPC is highly prevalent in the southern parts of China (30-250 per 100,000) including major cities like Hong Kong and Guangdong, accounting for 18% of all cancers in China. Intermediate incidence rates are found in Southeast Asia, the Mediterranean rim countries, coastal regions of Africa, and in the aboriginal populations of Alaska and Greenland. Large population of emigrants relocating from endemic areas to non-endemic areas such as United States, Canada and Europe also maintain their elevated risk status.
Where is NPC located in the human anatomy?
NPC is the most common cancer originating in the nasopharynx, the uppermost region of the pharynx (“throat”), behind the nose where the nasal passages and auditory tubes join the remainder of the upper respiratory tract. It is at the centre of the head and just underneath the brain also known as the skull base.
Epstien Barr Virus (EBV) and NPC
The Epstein-Barr virus (EBV), also called human herpesvirus 4 (HHV-4), is a virus of the herpes family, and is one of the most common viruses in humans. It is best known as the cause of infectious mononucleosis (mono or glandular fever). EBV infection normally occurs in early childhood. Over 95% of the population would have been infected by EBV at least once in their life time.
The association between EBV infection and NPC is well documented and cells with EBV genome are present in virtually all NPC cells. EBV was classified by the International Agency for Cancer Research (IARC) as a Class I carcinogen for NPC in 1997. The earliest forms of cancer cells, known as carcinoma in-situ (Stage 0)- classified by both World Health Organization (WHO) and American Joint Committee on Cancer (AJCC), (also found to contain copies of Epstein-Barr virus (EBV) DNA, indicating the important role of EBV in the early development of NPC.
While the consistent presence of EBV implies a critical role of the virus in the formation of NPC, many other co-factors are considered important in the genesis of NPC and they include age (increased age increased risk); gender (male is about 3 x more risk than female); exposure to environmental carcinogens (salted fish or preserved foods); genetic (family history with siblings or parents diagnosed of NPC) and/or immune deficiency.
Due to the consistent and definite presence of EBV DNA in all NPC cells, including those in early stage, EBV DNA has been shown to be an extremely sensitive and specific marker for NPC. Genetic based test using EBV DNA as target marker has been shown to be very useful in detection of NPC.