A kidney tumor is an abnormal area within the kidney. Doctors may use the terms mass, lesion, and tumor to describe this abnormal area. Tumors may be benign (not cancerous) or malignant (cancerous). The most common type of kidney mass is a fluid-filled area called a cyst. Not all cysts progress to cancer.
In adults, the most common type of kidney cancer is renal cell cancer, also called renal cell carcinoma. "Renal" means "related to the kidney."
According to estimates from the American Cancer Society (ACS), kidney cancer is the seventh most commonly diagnosed form of cancer for men and the twelfth most commonly diagnosed in women in the United States.
Types of Renal Cell Cancer
The five main types of renal cell cancer are:
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Clear cell carcinoma - cells appear very pale or clear under the microscope; it is the most common type of renal cell cancer.
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Papillary carcinoma - forms little fingerlike extensions, called papillae; is the second most common type of renal cell cancer. May also be called chromophilic (color-loving) because cells take up dye and appear pink under the microscope.
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Chromophobe renal carcinoma - called chromophobe (color-fearing) because cells appear pale under the microscope, like clear cell carcinoma, but are much larger and look different in other ways.
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Collecting duct renal carcinoma - very rare; begins in the kidney cells that form tubes and collect urine.
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Unclassified renal carcinoma - includes all renal cell cancers that can't be described using the other four categories.
Anatomy of the Kidney
The kidneys are two bean-shaped organs about the size of a fist. They are located on each side of the backbone, near the midback area.
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The kidneys serve several purposes, including:
- Filtering waste products and excess water from the blood to produce urine
- Draining the urine from the body
- Producing the hormones erythropoietin (helps increase the number of red blood cells), renin (helps regulate blood pressure), and calcitriol (helps to maintain normal calcium levels).
An otherwise healthy body can usually function well with one normal kidney in place of two should it become medically necessary to have one removed.