The significance of incidental diagnosing in relation to survival of renal cell carcinoma (RCC) patients is not known. A retrospective, population-based study was carried out in order to evaluate the survival of RCC patients, with emphasis on incidental diagnosing. Included in the study were all patients diagnosed with RCC in Iceland between 1971 and 1990. The tumours were classified and the extent of the disease staged by Robson's method. Crude probability of survival was evaluated for every stage, and multivariate analysis applied in order to determine prognostic factors. Out of 408 patients, 15% were diagnosed incidentally between 1971 and 1980 and 20% between 1981 and 1990 (p > 0.1), most often by intravenous urography. Only 5 tumours were detected incidentally by ultrasound techniques and 4 by CT scans. Crude five-year survival was 76% for stage I disease and 11% for stage IV disease. After correction for staging by multivariate analysis, incidental diagnosis and the year of diagnosis were not independent significant prognostic factors for mortality. As in many other studies, our data indicate that incidentally diagnosed RCCs are at a lower stage at the time of diagnosis. On the other hand, the results of our population-based study show that ultrasound and CT scanning have not significantly increased the number of incidentally diagnosed rumours. It is therefore not very surprising that surviving of RCC patients in Iceland has remained the same for the last two decades.
