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Geographic Distribution

Fig. 41.1. The geographic distribution of Burkitt's lymphoma in the tropics

Burkitt's tumor occurs predominantly in children (peak age 4 to 7 years) in the tropical zones of Africa, New Guinea and South America (Fig. 4.1). In parts of Africa, it accounts for from 30% to over 60% of all the malignant tumors of childhood. It is the commonest childhood malignancy in Ethiopia and much of the rest of Africa. In Latin America it accounts for 2-5% of childhood lymphomas. In Brazil, up to 13% of non-Hodgkins lymphomas are of the Burkitt type. Cases have been recorded in North America, Europe (particularly Spain), North Africa, the Middle East, Israel and elsewhere. In many areas it is more common in male than female patients, but this may reflect social trends rather than true incidence, because in most African and many other tropical hospitals male patients predominate. Many women are currently reluctant to seek modern medical aid, and this social pattern distorts statistics.

Burkitt's lymphoma is relatively rare in higher socioeconomic groups, and is uncommon below the age of one year and over 15 years. This differs from the pattern of Hodgkin's lymphoma, which increases steeply with age in industrialized western countries, a pattern which is less obvious in nonindustrialized regions. There is no evidence of a racial or tribal distribution, but Burkitt's lymphoma in Africa differs from the same lymphoma in other parts of the world. This may result from immunological stress from so many parasites, infections, and malnutrition. Burkitt's lymphoma spreads in a slow epidemic pattern. Time-space clustering has been reported. Unaccountable "outbreaks" have occurred in North America, where, for example, three young boys from a small Virginia town developed Burkitt's tumors between 1971 and 1975. The expected annual incidence for such a community would be one case per million children or one case every 200 years.

The tumor was once frequent in New Guinea, but it has decreased following the eradication of malaria and very few new cases have been seen in recent years. For a long time it did not occur on the island of Zanzibar, which was free of malaria although close to the coast of East Africa where the disease is common. In the tropics it is unusual to see the primary tumor in adults over the age of 20 and increasing age leads to increasing rarity in any population. It is less common in nontropical climates and also in those parts of the tropics where the temperature falls below 16°C (60°F) or where the average humidity is low. It is distributed across tropical Africa 10° above and below the Equator.

The geography of this tumor still fascinates researchers. Burkitt first observed that the tumor was related to temperature, minimum 16°C, and altitude, rarely occurring above 1,500 to 2,000 meters. Later, the tumor was related to rainfall, because of its high incidence in the wet tropics. From this came its association with malaria. It is usually said to be most common in endemic malarial areas, but is not confined to these regions. In Ethiopia the pattern is different. Amongst 39 Ethiopian children with Burkitt's lymphoma, 63% were from non-malarial areas and 76% came from above 1,500 meters. However, the homes of 95% of these patients were in areas with a mean average temperature above 16°C (61°F) and rainfall above 1,000 mm (39 in.). In South Africa there is a seasonal occurrence, with onset more likely in the rainy season regardless of race.

In South America there is a molecular difference between the lymphoma in Argentina and Chile (temperate) and Brazil (tropical). However, geography is more than climate and altitude, and soil collected from beneath several varieties of Euphorbia (gum) trees is known to contain substances which activate the Epstein-Barr virus (EBV), which is present in more than 95% of Burkitt's lymphoma in Africa. The rate of EBV association is lowest in North America (30%) and intermediate in South America (51%). (EBV is also an important finding in nasopharyngeal carcinoma).

Not unexpectedly, there is a high incidence of Burkitt's lymphoma in HIV-positive patients, further influencing it's current geographical distribution.

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Copyright: Palmer and Reeder