Schistosomal Eggs And Cancer

A definite association exists between the presence of eggs and carcinoma of the bladder, especially in squamous carcinoma. In Egypt, 82.5% of bladder tumors are associated with schistosomiasis (21), while in Malawi 67.1% of bladder tumors contain schistosome eggs (15). Ninety-four percent of bladder tumors in Zambia contain S. hematobium eggs, of which 72% are squamous carcinomas, 18% transitional carcinomas, and 10% adenocarcinomas or undifferentiated carcinomas (16). In Southern Iraq, schistosome eggs are present in 70% of squamous carcinomas, in 17.1% of transitional carcinomas, and in 12.8% of adenocarcinomas and anaplastic carcinomas of the bladder (22). A study from King Edward VIII hospital in Durban, South Africa reported a 61% association between chronic urinary schistosomiasis and bladder carcinomas in black patients (23).

A published series from Egypt showed squamous carcinomas to be the most common, with ratios of 70:25:5 between squamous carcinomas, transitional cell carcinomas, and adenocarcinomas (18). This contrasts sharply with squamous carcinoma, transitional carcinoma, and adenocarcinoma ratios of 5:94:1, respectively, reported in Western countries (24,25). It thus becomes evident that the ratio between transitional cell carcinoma and squamous carcinoma clearly differs when comparing tumor incidence in endemic and nonendemic areas with urinary bladder schistosomiasis. However, not all bladder malignancies in endemic schistosomiasis areas are associated with the parasite: 17.6% of bladder cancers in Egypt do not harbor eggs of S. hematobium (21). These cases represent either patients with schistosomiasis from nonbilharzial areas, patients with mild schistosomal disease or those in whom the disease had burnt itself out, or those patients who have been successfully treated and cured (21). In the treated group, tumors present at a later age, comparable with those in industrialized countries, as opposed to the younger age (46 yr) reported from endemic schistosomal areas (14).

Although the incidence of bladder malignancies, notably squamous carcinoma, is much higher in areas endemic for schistosomiasis, subtle differences occur within these endemic areas. Fripp and Keen (26) have reported a higher prevalence in the

Shangaan tribes of Mozambique and Eastern Transvaal, South Africa, especially in women, when compared to different ethnic groups of the Northern Transvaal. Egg load, naturally occurring carcinogens, dietary factors, and cultural or behavioral patterns may possibly explain these differences, although the nature of dietary factors remains elusive. One dietary factor that has been shown to be associated with raised incidence of bladder cancer in Ugandans is 3-hydroxyanthranilic acid. The source of this tryptophan derivative is the Matoke plantain, a staple food of some of the inhabitants. It should, however, be noted that this particular dietary factor is of importance in nonendemic S. hematobium areas (27).

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