Porth's Essentials of Pathophysiology, 4e

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Kidney and Urinary Tract Function

U N I T 7

MalignantTumors of the Kidney There are two major groups of malignant tumors of the kidney: embryonic kidney tumors (i.e., Wilms tumor), which occur during childhood, and renal cell carcinoma, which occurs in adults.  WilmsTumor Wilms tumor, also known as nephroblastoma, is one of the most common primary neoplasms of young chil- dren. It usually presents between 3 and 5 years of age and is the second most common malignant abdominal tumor in children. 4,32 It may occur in one or both kid- neys. The incidence of bilateral Wilms tumor is 6% to 7%, with children having a horseshoe kidney being at twice the risk. Histologically, the tumor is composed of elements that resemble normal fetal tissue: blastemic, stromal, and epithelial. An important feature of Wilms tumor is its association with other congenital anomalies, including aniridia (absence of the iris), hemihypertro- phy (enlargement of one side of the face or body), and other congenital anomalies, usually of the genitouri- nary system. Several chromosomal abnormalities have been associated with Wilms tumor. One Wilms tumor gene, WT1 located on chromosome 11, is a tumor-suppressor gene that regulates several other growth factor genes. 32 Wilms tumor usually is a solitary mass that occurs in any part of the kidney. It usually is sharply demarcated, variably encapsulated, and grows to a large size, dis- torting kidney structure (Fig. 25-16). The tumors usu- ally are staged using the National Wilms Tumor Study Group classification. 32 Stage I tumors are limited to the kidney and can be excised with the capsular surface intact. Stage II tumors extend into the renal capsule but can be excised. In stage III, extension of the tumor is confined to the abdomen, and in stage IV, hematogenous metastasis most commonly involves the lung. The common presenting signs are a large asymp- tomatic abdominal mass and hypertension. The tumor is often discovered inadvertently, and it is not uncom- mon for the parent to discover it while bathing the child. Some children may present with abdominal pain, vomit- ing, or both. Microscopic and gross hematuria is pres- ent in 15% to 25% of children. CT scans are used to confirm the diagnosis. 32 Treatment involves surgery, chemotherapy, and sometimes radiation therapy. Long-term survival rates have increased to more than 70% for all stages and to 91% to 96% for stages I through III. 32 Renal Cell Carcinoma Cancer of the kidney is the seventh leading malignancy among men and the twelfth among women, account- ing for about 3% of all cancers. 33 Incidence peaks between 55 and 84 years of age. 34 Renal cell carcinoma

accounts for approximately 80% to 90% of all kidney cancers. 4,5,33–35 Most renal cell carcinomas are sporadic, but about 5% are inherited. Inherited tumors tend to be multifocal and bilateral, and appear at an earlier age than sporadic renal cell carcinomas. A major advance in the understanding of renal cell carcinoma has been the realization that this neoplasm is not a single entity, but a collection of tumors that arise in different parts of the tubular or ductal epithelium. Clear cell carcinomas, so named because of their high cyto- plasmic lipid content, accounts for 70% to 80% of all renal cell carcinomas. 5 They arise from proximal tubular epithelial cells and appear as solitary unilateral lesions located predominantly in the renal cortex (Fig. 25-17). Papillary carcinomas, which are characterized by a pap- illary growth pattern, account for another 10% to 15% of renal cancers. 5 Thought to arise from the proximal tubules, they can be multifocal and bilateral. The cause of renal cell carcinoma remains elusive. Epidemiologic evidence suggests a correlation between heavy smoking and kidney cancer. 33,34 Obesity also is a risk factor, particularly in women. Additional risk fac- tors include occupational exposure to petroleum prod- ucts, heavy metals, and asbestos. 5 The risk for renal cell carcinoma also is increased in persons with acquired cystic kidney disease associated with chronic renal insufficiency. Kidney cancer is largely a silent disorder during its early stages, and symptoms usually denote advanced FIGURE 25-16. Wilms tumor. A cross-section of a pale tan neoplasm (arrow) attached to a residual portion of the kidney. (From Jennette JC.The kidney. In: Rubin R, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of Medicine. 6th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott Williams &Wilkins; 2012:805.)