Schistosomiasis and the risk of bladder cancer in Alexandria, Egypt

The relationship between history of schistosomiasis and bladder cancer risk was investigated using data from a case-control study conducted between January 1994 and July 1996 in Alexandria, Egypt. Cases were 190 subjects with incident, histologically confirmed invasive cancer of the bladder, and controls were 187 subjects admitted to hospital for acute, non-neoplastic, non-urinary tract conditions. Eighty-six cases (45%) vs 69 controls (37%) reported a history of urinary schistosomiasis. The corresponding multivariate odds ratio (OR) of bladder cancer - after allowance for age, sex, education, smoking, other urinary infections and high-risk occupations - was 1.72 (95% confidence interval (CI) 1.0-2.9). The ORs were 0.22 (95% CI 0.1-0.4) for intestinal schistosomiasis and 0.32 (95% CI 0.1-1.9) for schistosomiasis of other types. The OR for urinary schistosomiasis was higher in subjects who were younger at first diagnosis (OR of 3.3 for < 15 years) and in those with a long time since first diagnosis (OR of 3.0 for ≤ 35 years). The ORs were 15.8 for male ever-smokers with a history of urinary schistosomiasis, compared with never-smokers without such a history, and 3.2 for men ever-infected with urinary Schistosoma haematobium and ever-employed in high-risk occupations, compared with those never-infected and with no high-risk occupational history. This study confirms that clinical history of urinary schistosomiasis is significantly, but modestly, associated with increased bladder cancer risk, explaining some 16% of bladder cancer cases in this Egyptian population. A case-control study conducted in Alexandria, Egypt, in 1994-96, investigated the association between a history of schistosomiasis and the risk of bladder cancer. Egypt's bladder cancer rate is the highest in the world. Enrolled were 190 adults with incident, histologically confirmed invasive cancer of the bladder and 187 controls admitted to the same hospitals for acute causes unrelated to neoplasms or the urinary tract. 86 cases (45%) and 69 controls (37%) reported a history of urinary schistosomiasis. After adjustment for age, sex, education, smoking, high-risk occupations, and other urinary infections, the odds ratio (OR) for bladder cancer risk was 1.72 (95% confidence interval (CI), 1.0-2.9). The ORs were 0.22 (95% CI, 0.1-0.4) for intestinal schistosomiasis and 0.32 (95% CI, 0.1-1.9) for other types of schistosomiasis. The risk for urinary schistosomiasis was higher in subjects under 15 years of age at first diagnosis (OR, 3.3), suggesting a duration-risk relationship. The ORs were 15.8 for male ever-smokers with a history of urinary schistosomiasis and 3.2 for men ever-infected with Schistosoma haematobium and ever-employed in a high-risk occupation. Other studies that have used eggs in urine or histologic samples, rather than self-reported clinical history of urinary schistosomiasis, have produced similar results. Based on the findings of this study, a clinical history of urinary schistosomiasis accounts for an estimated 16% of bladder cancer cases in this Egyptian population. Tobacco smoking is a far greater risk factor for bladder cancer in Egypt.