Kidney Cancer: The Basics

What is the Kidney?

The kidneys are two bean-shaped organs that are located in the back of the abdomen, and that have many important functions essential for life. Among the most important are filtrating the blood, removing waste products from the blood and ensuring that the electrolytes within the blood are correctly balanced. In addition, the kidneys produce erythropoietin, a hormone responsible for the production of (the oxygen carrying) red blood cells. Each of the kidneys can be divided into two main functional parts. The outer region of the kidney is called the cortex The cortex consists of a series of tubes (called collecting tubules) and is responsible for the filtration of blood.. The inner region of the kidney is called the renal pelvis. The renal pelvis contains medullary pyramids that collect the filtrate (urine) from collecting tubules in the cortex and send it through the ureters to the urinary bladder. Different types of cancers develop from the two different regions of the kidneys.

The kidneys are located in the posterior aspect of the abdomen, directly in front of where the lowest ribs can be felt on a person's back. A physician can palpate them in the abdomen at times, though often only if the kidney is enlarged or has a mass on it.

What is 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.

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