Comparison of cancers of the oral cavity and pharynx worldwide: etiological clues
Introduction
Cancers of the oral cavity and pharynx combined account worldwide, after the exclusion of nasopharynx, for approximately 220,000 new cases per year in men (5% of all cancers) and 90,000 in women (2% of all cancers) [1]. In some parts of Asia (i.e. south-central Asia), world-standardised incidence rates for cancers of the oral cavity and pharynx exceed in men those for any other tumours.
After many-year decline, incidence and/or mortality for cancers of the oral cavity and pharynx have been rising in the last two or three decades in many developed countries, particularly in southern and eastern Europe [2], though not, for instance, in US whites [3], [4]. Such increases are chiefly attributable to rises in the consumption of tobacco and/or alcoholic beverages [5]. An influence of dietary factors [5] and some infectious agent (e.g. human papillomavirus [6]) is also possible. Relatively little is known, however, on trends of cancer of the oral cavity and pharynx in countries outside Europe and the Americas [7], [8], [9] where betel chewing [10] and, possibly, dietary deficiencies [11] play a major role.
A comparison between oral cancer and pharyngeal cancer has seldom been attempted [1], [12], [13], due to the difficulty of assigning a site of origin, particularly in advanced cancers. However, there appears to be a substantial difference in the distribution of these two sites worldwide. In order to provide etiological clues, we compared, in the present article: (1) the distribution of oral and pharyngeal cancer, by means of incidence data from late 1980s to early 1990s which are available from an unprecedented variety of areas worldwide [4]; and (2) incidence trends of these two sites over the last 30 years or so in selected areas which are representative of parts of the world where the determinants of cancer of the oral cavity and pharynx vary substantially [3].
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Materials and methods
Cancers of the oral cavity and pharynx include different tumours. Cancers of the lip (International classification of diseases [ICD]-9=140), of the salivary glands (ICD-9=142), and of the nasopharynx (ICD-9=147) were not assessed in our review on account of differences in histopathology, aetiology, and, for nasopharyngeal cancer, the substantial restriction of such neoplasm to some Asian areas [14]. Thus, we concentrated on oral cavity (i.e. tongue, ICD-9=141; gum, floor and other parts of the
Results
Incidence rates of cancers of the oral cavity and pharynx for 1988–92 by sex are shown for 49 areas (Table 1, Fig. 1). Table 1 also includes sex-specific oral/pharyngeal ratios.
In men in the Americas and the Australian Continent the highest rate (i.e. 17.8 per 100,000) were found in blacks in the USA, followed by Brazil, Porto Alegre, and Puerto Rico. The lowest rates were observed in Colombia, Cali, and Costa Rica, with an approximately three-fold variation. Corresponding range is narrower in
Discussion
In 1988–92 incidence rates for the combination of cancers of the oral cavity and pharynx worldwide varied approximately 20-fold in both sexes. The systematic comparison between oral and pharyngeal cancer discloses several interesting differences with respect to the relative frequency of these two sites, oral/pharyngeal ratios by gender, and incidence trends over the last two or three decades.
The possibility of some degree of misclassification of site of cancer origin should be kept in mind.
Acknowledgements
The authors wish to thank Dr. Jacques Ferlay for providing data and Mrs. Anna Redivo for editorial assistance. This work was supported by grants from the Italian Association for Research on Cancer.
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