Cancer of the kidney—etiology, epidemiology, and pathology

Renal adenocarcinoma represents approximately 1% of all malignancies exclusive of skin cancer. It is extremely rare in children or young adults and its incidence is over three times as great in men as in women. Familial occurrence is rare although there is a high frequency in patients with Lindau's disease. Naturally occurring renal adenocarcinoma is uncommon in lower animals except in rare instances of familial tumors in rodents. However, in laboratory animals renal adenocarcinomas are readily induced by a variety of carcinogens including chemical, physical, and viral agents. Implications of these studies to the epidemiology of human renal adenocarcinoma are discussed. Human, as well as naturally-occurring and experimentally-induced renal adenocarcinomas in lower animals, arise from the proximal convoluted tubule and are remarkably similar histologically and electronmicroscopically. Typically, these tumors are composed of cells which are clear or granular, a function of the cellular content of glycogen, lipids, and cytoplasmic organelles, and may be arranged in solid, cystic, trabecular, tubular, or papillary patterns. Rarely (1.8% of all renal adenocarcinomas) they are sarcomatoid mimmicking fibrosarcoma, rhabomyosarcoma, or liposarcoma. These various histologic patterns are poorly related to survival except for the sarcomatoid tumors which are regarded as highly aggressive. Renal cortical parenchymal tumors resembling the renal adenocarcinoma but less than 3 cm in diameter have historically been regarded as adenomas because of their low frequency of metastases. Based on the many points of similarities between the renal adenocarcinoma and the so-called renal adenoma, it is postulated that these tumors are simply small renal adenocarcinomas which have not yet grown large enough to metastasize.