The Diversity Of Renal Cancers

Cancers of the kidney account for a few percent of all human malignant tumors. There is a large variety of tumors in this organ, which can serve well to illustrate the diversity of human cancers (Table 15.1).

Most cancers in the kidney are carcinomas, which have traditionally been distinguished by their histological appearance (Figure 15.1). The incidence of renal cell carcinomas (RCC) in industrialized countries is «10:100,000/year. Most are thought to originate from different parts of the nephron. Clear-cell carcinomas, the most frequent subtype, are thought to originate from proximal tubuli, which are located in the renal cortex. Because it is the most common subtype (70 - 80% of all cases), it is also called 'conventional renal cell carcinoma'. Papillary cancers also arise from the same region, perhaps from nephrogenic rests persisting from fetal development. In this regard they resemble Wilms tumors (^11), but papillary renal carcinomas are derived from more mature cells at a later stage of development.

Table 15.1. Some benign and malignant tumors found in the kidney

Tumor type (remarks) Angiomyolipoma (benign) Chromophobic carcinoma (malignant) Clear cell renal carcinoma (malignant) Fibrosarcoma (malignant, adult) Hyperproliferative cysts (benign) Lymphoma (malignant) Medullary carcinoma (malignant) Metastases (malignant) Metanephric adenoma (benign) Oncoytoma (benign) Papillary carcinoma type I (malignant) Papillary carcinoma type II (malignant) Papillary-tubular adenoma (benign) Rhabdomyosarcoma (malignant, pediatric) Urothelial carcinoma of the renal pelvis (malignant) Wilms tumor (malignant, pediatric)

Figure 15.1 Histologies of renal cancers Histological aspects of clear cell (top left), papillary (top right), and chromophobic (bottom left) renal carcinomas and of non-malignant oncocytoma (bottom right).

Chromophobic carcinomas very likely originate from the distal tubuli, as do benign tumors named oncocytomas. The rare aggressive Ductus-Bellini carcinomas are derived from the collecting duct in the medulla of the kidney. Since the renal pelvis is lined by urothelium, like the bladder, urothelial cancers can also develop in the kidney (^14). There are also tumors from mesenchymal tissues, such as moderately frequent benign angiomyolipomas and rarer malignant sarcomas. Moreover, as an organ with an extended capillary system, the kidney is a site for metastases from carcinomas from distant organs and for lymphomas.

The variety of cancers in the kidney creates a certain predicament for therapy. Kidney tumors are nowadays usually detected by physical imaging techniques such as ultrasound or computer tomography. These give a good indication of the extension of the tumor, but no definitive information on the tumor type. This has to rely on histological and molecular investigations. Since biopsies on kidney cancers are regarded as problematic, non-invasive molecular assays for this purpose would certainly be very helpful (^-21.4).

Traditionally, when a tumor was present, the entire kidney was removed. Today, partial nephrectomy is often performed, if histological and molecular markers indicate that a tumor recurrence is unlikely. This is evidently a good option for benign tumors like oncocytoma. Partial nephrectomy can also be performed in patients with small malignant tumors and an increased likelihood of failure of the other kidney, e.g. in the context of an inherited cancer syndrome (—>15.3). For the choice of treatment, precise identification of the tumor variety is, of course, imperative.

For localized renal carcinomas, removal of the tumor by surgery is usually curative. In contrast, chances for a cure become minimal, once renal carcinomas have metastasized, since all varieties responding badly to currently available chemotherapy. In individual patients, therapies directed at stimulating the immune system can lead to excellent responses, but in a rather unpredictable fashion (^■15.6).

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