Kidney Cancer

The definition of a tumor is a mass of abnormally growing cells. Tumors can be either benign or malignant. Benign tumors have uncontrolled cell growth, but without any invasion into normal tissues and without any ability to spread to distant parts of the body. A tumor is called malignant, or cancer, if tumor cells gain the propensity to invade tissues and spread locally as well as to distant parts of the body. In this sense, kidney cancer occurs when cells in either the cortex of the kidney or cells in the renal pelvis grow uncontrollably and form tumors that can invade normal tissues and spread to other parts of the body.

Cancers are described by the types of cells from which they arise. Again, when discussing kidney cancer, the cortex and the renal pelvis must be discussed separately. In the kidney cortex, the vast majority of cancers arise from the cells that line the collecting tubules, more specifically, the proximal tubules. Cancers that develop from lining such as this are called carcinomas. In this case, they are called renal cell carcinomas. Over 75% of renal cell carcinomas are called clear cell carcinomas, named after the characteristics they display when looking at them under the microscope. Other classifications, in decreasing order of prevalence, include chromophilic, chromophobic, oncocytic, and collecting duct cancers. However, it does not appear that these various types of renal cell carcinoma differ in presentation or prognosis.

Cancers of the renal pelvis, or medulla, are uncommon. Over 90% of cancers that develop in the renal pelvis are called transitional cell carcinomas. They are so named because they develop from cells that line the renal pelvis and upper ureters.

Am I at risk for kidney cancer?

Kidney cancer occurs in approximately 31,000 Americans per year and cancers of the renal pelvis will occur in approximately 3,000 Americans per year. Most patients are diagnosed between the ages of 50 and 70. Kidney cancer is more common in men than women, with an equal preponderance in whites and blacks. A number of risk factors are associated with an increased probability of renal cell cancer: The most prominent risk is cigarette smoking. Persons who smoke have twice the risk of developing kidney cancer as people who don’t smoke, and smoking is directly responsible for up to one out of every three cancers. The risk for kidney cancer also increases fourfold in persons with a first-degree relative who had kidney cancer. Other, less-proven risk factors include obesity (especially in women), analgesic abuse, high blood pressure, and several uncommon hereditary diseases, including von Hippel-Lindau disease and polycystic kidney disease.