Incidental detection of renal cell carcinoma (RCC) is increasing and is associated with better survival from the malignancy, according to a population-based study conducted in Iceland.
Using centralized databases, Tomas Gudbjartsson, MD, PhD, of the Landspitali University Hospital in Reykjavik, and collaborators conducted a retrospective study of all living patients diagnosed with RCC in Iceland from 1971 to 2005. In 2005, the Icelandic population was estimated to be about 300,000. The researchers compared survival of patients with incidentally diagnosed and symptomatic RCC.
Of 910 patients diagnosed with RCC during the 35-year observation period, 254 (27.9%) were diagnosed incidentally, Dr. Gudbjartsson’s team reported in The Journal of Urology (published online ahead of print).
The incidental detection rate rose significantly from 11.1% in 1971 through 1975 to 39.2% in 2001 through 2005. During those same intervals, the incidence increased significantly among male subjects, but only during the last five study years among female subjects. Mortality remained unchanged for males and females. Tumors diagnosed incidentally on average were 2.6 cm smaller than symptomatic tumors, and diagnosed at lower stage and lower grade than symptomatic tumors. TNM stage was by far the strongest independent predictor of survival, the researchers found. Compared with patients with stage I tumors, those with stage IV tumors had a 17.7 times increased risk of disease-specific mortality.
After adjusting for age, year of diagnosis, TNM stage, and other confounders, patients with symptomatic RCC had a 40% increased risk of disease-related death than those with incidentally diagnosed RCC, but the risk was increased significantly only for patients with systemic, not local, symptoms (47% vs. 31%).
Investigators also observed a shift in how incidentally diagnosed tumors were detected. For the study period overall, the most common modes of detection were abdominal ultrasound (29.5%) and computerized tomography (CT, 28.3%) performed for unrelated complaints or diseases. After 2000, CT accounted for 55.4% and ultrasound accounted for 26.5% of diagnoses. The proportions were 75% and 12.5%, respectively, in 2005.
The current study builds on a previous study by the same researchers, who six years earlier reported in Urology (2005;66:1186-1191) on a population-based study of 701 RCC patients in Iceland, where incidental detection did not reach statistical significance as an independent prognostic factor of survival. Dr. Gudbjartsson’s team stated that, to their knowledge, the current study and the one published in 2005 are the only population-based studies to have analyzed the effect of incidental detection on survival.
The authors noted that their most recent results might be explained by an epidemiological variable that differs between incidentally and symptomatically diagnosed patients. For example, the two groups might interact with the health care system at different frequencies. In addition, better survival in the incidentally diagnosed group could be due to possible lead time and stage migration bias in that tumors detected sooner “may be less invasive and have lower malignancy potential, resulting in more favorable prognosis.”
Biological differences between incidentally and symptomatically detected tumors are another possibility.
According to Dr. Gudbjartsson, Professor of Surgery at the University of Iceland in Reykjavik, the study helps to define the role of incidental detection in RCC as an independent and favorable prognostic factor, which is important since the majority of RCC’s are now detected incidentally