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Introduction:
Nasopharyngeal cancer is a malignant tumor involving the nasopharyngeal epithelial lining.
Study of epidemiology of nasopharyngeal carcinoma makes an interesting reading. Extensive
epidemiological studies conducted during the last 40 years have thrown lot of insights in
the etiopathogenesis of this disease. This is one of the malignant conditions the causation
of which a virus has been implicated (Epstein Barr virus). NPC (hereafter in this article
nasopharyngeal carcinoma will be addressed thus) has demonstrated unique epidemiological features
which include the most obvious regional, racial and familial predispositions.
Distribution:
Nasopharyngeal carcinoma is unique in its virtually endemic distribution confined to certain areas
of the globe. Classically it is most common in the southern parts of China. In fact the Guangdong
province of southern china shows the highest incidence (up to 100 / 100000) That is
the reason for its another name "Canton tumor". In the year 2002 alone China accounted for nearly 50%
of newly diagnosed cases of NPC. Studies have also revealed significant differences in the incidence
rates of NPC between Northern and southern parts of China.
Gender distribution:
Incidence of NPC is significantly higher in males than in females. It is about 3 times more common in
males than females. Male predominance has been documented in both endemic and low incidence areas.
Age distribution:
Age distribution varies according to the incidence rates. In low incidence areas it increases with age,
where as in endemic areas the incidence increased after the age of 30 and peaked at 50 years of age.
In medium incidence areas the incidence showed a minor peak at adolescent age groups.
Racial distribution:
Studies have shown that the incidence of NPC's is maximum in xanthoderms (yellow skinned individuals).
Melanoderms come next (dark skinned races) while caucasians (white skinned) were found to be least prone.
Study of data pertaining to incidence of NPC in migrants proved that people from endemic areas retained their
predisposition to NPC even when they migrate to low incidence areas like U.S.
Familial predisposition:
Incidence of NPC shows discernible familial predisposition. It is more so in families living in high incidence
areas like southern china.
Studies have shown that there has been a progressive decline in the incidence of NPC even in endemic areas. Studies
have revealed a specific decline in the incidence of keratinizing squamous carcinoma because of decreasing incidence
of smoking in these areas. On the contrary Non keratinizing squamous cell carcinoma variety did not show any decline
in incidence. Considering the high incidence of Epstein Barr virus infection, the incidence rate of NPC is not so
alarming. This could be attributed to the fact that in addition to EB virus infection other factors are also
necessary. NPC should hence be considered to be a multifactorial disease.
Etiological factors (possible):
1. EB virus infection
2. Salty fish and pickled food: Ingestion of salty fish and pickled food have been attributed as one of the causative
features. These food stuffs contain N-nitrosamine which is a known carcinogen. It has also been shown increased
ingestion of fresh vegetables and fruits can reduce the risk of NPC due to beneficial effects of antioxidant and
antinitrosamine components.
3. Smoking / dringking: Have shown to be risk factors involved particularly in Non keratinizing varieties of squamous
cell carcinoma.
4. Hereditary susceptibility: Studies have shown tha HLA - A2 - Bw46 and B17 have shown increased incidence of NPC
by 2 - 3 fold.
5. Risks posed by traditional chinese medicine:Studies have shown that increased use of chinese traditional medicine
have increased the risk of NPC by 3 fold. Some of the ingrediants used in chinese traditional medicine have been shown
to activate the latent EB virus infection
6. Exposure to carcinogens like formaldehyde, wood dust, and Nickel have shown to increase the risk of NPC
7. More recently inviduals with chronic upper air way disease are more prone to risk of acquiring NPC because bacteria
present in the upper airway converts nitrate to nitrite which is a carcinogen
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