Pathology of renal tumors in adults. Molecular biology, histopathological diagnosis and prognosis.

Malignant renal tumors constitute 3% of human cancers, although their frequency differs greatly in various areas. Since the fifties, the incidence of renal cancers has been increasing, but at the some time the prognosis has been improving. In particular, in the last years, several new treatment modalities have been introduced, relying on the understanding of renal cancer biology. The identified etiological factors include smoking, increased body mass, dietary factors and chronic renal disease. There are several renal tumor types differing in morphology, molecular genetics and biology. Inactivation of the VHL gene leads to formation of the most frequent form in adults, namely clear cell carcinoma. The VHL gene product, a component of an ubiquitin-ligase complex, regulates expression of several genes. Papillary carcinomas depend mainly on the HGF receptor gene (c-Met) activating mutations. At least two types of papillary carcinomas exist, which have different morphology and prognosis. The molecular biology of chromophobe carcinoma and oncocytoma is poorly understood. Differential diagnosis of these tumors is particularly difficult and may require extensive immunohistochemical and molecular studies. Collecting duct carcinoma and medullary carcinoma are extremely aggressive but rare tumors. Some renal tumors have been described or recognized only relatively recently; these newer entities include multilocular cystic clear cell carcinoma, spindle cell papillary mucinous carcinoma, tubulocystic carcinoma, renal epithelial and stromal tumor, epithelioid and oncocytic angiomyolipoma. Besides histological typing, the prognostic factors include tumor stage, grade and several immunohistochemical and molecular markers that are currently under elaboration. The improved prognosis in renal cancer depends on earlier detection, but also on refinement of therapeutic methods. Small tumors may currently be treated by partial nephrectomy or radiofrequency ablation and larger ones by a laparoscopic approach. All these methods seem to give satisfactory results with low morbidity and mortality rates. Renal carcinoma is notorious for its low sensitivity to chemotherapy and radiotherapy. For several years, immunological treatment with IL-2 and INF-alpha was the only adjuvant therapy method. However, recently several new drugs have been introduced; they act on tyrosine-kinase receptors, VEGF, c-Met or mTOR pathway. With this progress, perfect understanding of renal tumor biology and exact histological diagnosis have become of prime practical importance.