A questionnaire study was performed among 23,209 dialysis patients in 589 institutions together with a retrospective study at Keio University Hospital to determine the risk of malignancy and factors affecting the risk ratio in dialysis patients. The incidence and mortality were 1.4-fold and 1.9-fold higher in dialysis patients than the expected rates in the general population. Incidence and mortality were 1.9-fold and 2.6-fold higher in males than in females. The risk ratios were remarkably high in university hospitals, followed by public hospitals. However, there was no significant difference between those in private hospitals and in the general population. The incidence was very high during the first 6 months of dialysis treatment and rather low in the 7th-10th year. The risk ratio of malignancy was higher in younger patients. Beyond the age of 60, the influence of age was greater than that of renal failure. Malignancies of the digestive organs were frequent and constituted 56% of all malignancies. Frequencies of malignancy in the liver, colon, rectum, bladder and kidney were higher than expected, whereas in the pancreas the frequency was lower than expected. Metastasis of malignancy was observed in 30% of the cases. Our study demonstrated a slight to moderate overall increase in the risk of malignancy and a widely differing risk ratio of malignancy by organ involved, sex, age, hospital group, epidemiological index and length of dialysis treatment in a large single racial population of maintenance dialysis patients.
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