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Nineteen de-novo tumors in cystoplasties using ileum or colon have been reported. Frequency, localization, latency period, and histology suggest a similar origin and a similar cancer risk to that seen after ureterosigmoidostomy. The cause of this form of carcinogenesis seems to be the combination of proliferative activity at the urointestinal anastomosis, carcinogenic urine, and the presence of transitional epithelium. Epidermal growth factor and its receptor, transforming growth factor α, carcinogens in urine, and oncogenes and suppresor genes could be of importance in multistep carcinogenesis, whereas urinary nitrosamines do not seem to play a major role, if any. Regular endoscopie evaluation is necessary in all forms of urinary diversion 5–10 years after the operation.