Incidence of nasopharyngeal carcinoma in Belgrade during the period 1991 – 2005 Incidencija karcinoma nazofarinksa u Beogradu za period 1991 – 2005 . godine

Background/Aim. Nasopharyngeal carcinoma (NPC) is a relatively rare malignant disease, of which 80 000 individuals become ill around the world annually, which amounts to 0.7% of all carcinomas. The aim of this descriptive study was to analyze NPC incidence in Belgrade (the capital city of Serbia, with about 1.6 milion inhabitants) during the period 1991–2005. Methods. In data analysis, crude rates age and sex specific rates, and standardized incidence rates were used. Standardization was performed by a direct method, using world population as the standard. Results. In Belgrade, during the observed 15-year-period, the number of new NPC patients totaled 118, of which 86 (72.9%) were male and 32 (27.1%) were female. The average standardized incidence rate for men was 0.52 per 100 000 and for women 0.16 per 100 000. In both sexes the incidence was very low before 40 years of age. In men, the greatest incidence rate of NPC was in the 50–59 years age group, and in women in those 60 and more years old. Furthermore, undifferentiated carcinoma of nasopharyngeal type was 3.6 times more often in comparison to squamous cell carcinoma. Conclusion. Belgrade belongs to a region with a low incidence rate of NPC. Further investigations are needed to explain higher frequency of undifferentiated carcinoma of nasopharyngeal type than squamous cell carcinoma.


Introduction
Nasopharyngeal carcinoma (NPC) is a relatively rare malignant disease, of which 80 000 individuals become ill around the world annually, which amounts to 0.7% of all carcinomas 1 .The incidence of NPC varies among the coun-tries of the world, as well as within the countries themselves 2 .The greatest standardised incidence rate of NPC of > 20 per 100 000 residents was recorded among the Chinese population living in southeast China, in the province of Guangdong.A moderately high incidence rate of NPC of 1-20 per 100 000 inhabitants was recorded in other parts of Nešić V, et al.Vojnosanit Pregl 2009; 66(6): 473-476.
China, in the peoples of South-East Asia (Thais, Vietnamese, Malays, and Filipinos), in the Arabs of North Africa and in the inhabitants of the Arctic (Intuits living in Alaska).In western countries and other parts of the world, the standardised incidence rate of NPC is less than 1 per 100 000 residents 1,[3][4][5] .
The aim of this study was to analyse NPC incidence in Belgrade during the period 1991-2005, as well as to determine the extent of undifferentiated carcinoma of nasopharyngeal type (UCNT) and squamous cell carcinoma (SCC) among the patients 6,7 .

Methods
The study included new patients suffering from NPC, living in Belgrade (the capital city of Serbia, with about 1.6 million inhabitants), in whom illness was diagnosed during the period 1991-2005 at the medical institutions in Belgrade (Institute of Otorhinolaryngology and Maxillofacial Surgery of the Clinical Centre of Serbia, Military Medical Academy and three Clinical Medical Centres in Belgrade).
Average number of Belgrade inhabitants (by sex and age) in the census years 1991 and 2002 was used as denominator for calculation of incidence 8 .In data analysis, crude rates, age and sex specific rates, and standardized incidence rates were used.Standardization was performed by a direct method, using world population as standard 9 .

Results
During the observed 15 year period, the number of new patients suffering from NPC totalled 118, of which 86 (72.9%) were men and 32 (27.1%) women (Table 1).The average standardized incidence rate for men was 0.52 per 100 000 (ranging from 0.33 to 0.67), and for women was 0.16 per 100 000 (ranging from 0.06 to 0.30).The rates fluctuated during the period, and a specific trend was not observed.
In both sexes the incidence was very low before 40 years of age.In men, the greatest incidence rate of NPC was in the 50-59 years age group, and in women in those 60 and more years old (Table 2).
On the basis of histopathological diagnosis, in both sexes UCNT was more frequent than SCC -3.1 times more frequent in men, and 5.4 times more frequent in women.The frequency of UCNT in men was 2.4 times of that in women.SCC was 4.2 times more frequent in men in comparison to women.Our results demonstrated that the average standardized incidence rate of NPC in Belgrade was similar to that of some countries of the Western Europe and USA (Table 3).

Discussion
In Belgrade, as in most of the countries of Europe, carcinomas of the nasopharynx constitute less than 1% of all malignant tumours 4 .Data for Belgrade show that its population is one with low NPC incidence (0.52 per 100 000 for men and 0.16 per 100 000 for women) such as populations of some countries of the Western Europe and North America [10][11][12][13][14] .
In all studies published until now, as in the present one, men were shown to suffer from NPC more frequently than women.Thus, in high risk populations, for example among Chinese living in Singapore, the sex ratio (men in comparison to women) was 2.3:1 2 , and in Hong Kong it was 2.6:1 15 .
According to the data from the "Eurocare" study, which included new patients suffering from NPC during the period 1978-1989, 67% of all patients with NPC were men, and 33% were women, which is similar to our results (73% men and 27% women) 4 .
Nasopharyngeal carcinoma is usually more frequent in older people.The occurrence of patients younger than 55 years varies from 25% in Denmark to 55% in Spain and Slovakia 4 .In Belgrade population 51% of NPC cases were less than 55 years old, and the greatest incidence rate was in a 50-59 years age group for men and in the 60 years plus age group for women.The greatest frequency of NPC in Caucasians is between 55-65 years of age, in Chinese between 40 and 45 years of age, in Arabs from the Maghreb countries, and in Indians from 10 to 20 years of age and from 55 to 65 years of age 2,16 .
The most interesting finding of the present study is a much higher frequency of UCNT compared to SCC.The occurrence of UCNT varies for both men and women, and percentage of UCNT among all NPC cases ranged from 30% in Scandinavia to 50% and more in the countries of Southern Europe 4 .In Belgrade population UCNT was 3.6 times as that of SCC.Reasons for such variations in the UCNT frequency can be explained either by genetic differences or by differences in the exposure to environmental factors related to these two types of NPC, or by both.