Nasopharyngeal carcinomas are another carcinoma found in association with reactivation of latent Epstein-Barr Virus. The exact mechanisms of association are unknown and the epidemiology is as follows:
Descriptive
Epidemiology
Incidence
Nasopharyngeal
cancer incidence rates are less than 1 per 100,000 in most populations.
In persons of Chinese descent, these rates are much higher, with elevated
cases in southern China. Isolated northern populations such as Eskimos
and Greenlanders also show higher incidence. Southeast Asian populations
show lower incidences, Japan and Northern China show almost none.
In Tunisia, Morocco, and Algeria there is moderate incidence. There
is also moderate incidence in Kuwait, the Sudan, parts of Kenya, Uganda,
and in Israel (4).
Age and
Sex
Men are
twice as likely to develop nasopharyngeal carcinoma as women (4).
The rates general increase from ages 20 to around 50. In the United
States, African-Americans develop NPC at a higher rate than whites until
middle age, with a sevenfold increase in the under 20 age group.
Chinese-Americans comprise the majority of NPC patients, with a peak similar
to the general rates (4).
Environment
Mortality
rates in Taiwan have shown an association between NPC and salt workers
and miners. Studies related to nutrition and diet have seemed to
confirm an association between eating highly salted foods and NPC.
Vitamin C deficiency at a young age may also be a contributing factor.
In the United States, those workers who were exposed to fumes, smoke, and
chemicals were at highest risk, implying a role for chemical carcinogenesis
(4).
Genetic
Factors
A study
of MHC haplotypes revealed a genetically distinct subpopulation in Southern
China, which may account for the highest incident areas. Chinese
NPC patients were shown to have an increased frequency of HLA-A2 and a
decreased frequency of antigens detected at the second locus. This
blank was named Sin-2 (or B46). This haplotype, A-2-B-Sin-2 was shown
to have an elevated relative risk (4).
Study of MHC haplotypes in other populations has indicated a possible genetic
predisposition as well.