Morphological findings in frozen non-neoplastic kidney tissues of patients with kidney cancer from large-scale multicentric studies on renal cancer.

There are unexplained geographical variations in the incidence of kidney cancer with the high rates reported in Baltic countries, as well as eastern and central Europe. Having access to a large and well-annotated collection of "tumor/non-tumor" pairs of kidney cancer patients from the Czech Republic, Romania, Serbia, UK, and Russia, we aimed to analyze the morphology of non-neoplastic renal tissue in nephrectomy specimens. By applying digital pathology, we performed a microscopic examination of 1012 frozen non-neoplastic kidney tissues from patients with renal cell carcinoma. Four components of renal parenchyma were evaluated and scored for the intensity of interstitial inflammation and fibrosis, tubular atrophy, glomerulosclerosis, and arterial wall thickening, globally called chronic renal parenchymal changes. Moderate or severe changes were observed in 54 (5.3%) of patients with predominance of occurrence in Romania (OR = 2.67, CI 1.07-6.67) and Serbia (OR = 4.37, CI 1.20-15.96) in reference to those from Russia. Further adjustment for comorbidities, tumor characteristics, and stage did not change risk estimates. In multinomial regression model, relative probability of non-glomerular changes was 5.22 times higher for Romania and Serbia compared to Russia. Our findings show that the frequency of chronic renal parenchymal changes, with the predominance of chronic interstitial nephritis pattern, in kidney cancer patients varies by country, significantly more frequent in countries located in central and southeastern Europe where the incidence of kidney cancer has been reported to be moderate to high. The observed association between these pathological features and living in certain geographic areas requires a larger population-based study to confirm this association on a large scale.