Familial aggregation of urinary system tumors in a region with endemic nephropathy.

In hyperendemic villages in the Vratza district of Bulgaria, 193 patients with urinary system tumors (UST) were diagnosed during 1965 to 1976. A tendency towards familial aggregation was revealed when the patients were compared with two groups of controls, namely, patients with tumors other than UST and healthy persons. Each control group consisted of 193 persons matched by sex, age, and place of birth. This tendency was observed in all relatives who lived together as well as in those related by blood. The probability of having relatives with UST was 2.5 times higher than could be expected as chance occurrence among UST patients than among the controls. The UST cases also had significantly more relatives with endemic nephropathy than did the controls. The familial clustering of both UST and nephropathy in the endemic region is considered another clue to their common etiology.