The kidneys are a pair of organs in the rear part of the abdomen, on either side of the spine. They are a part of the urinary tract. The National Cancer Institute reports that 20,000 men and 12,000 women are diagnosed with kidney cancer each year. Kidney tumors form when cancer cells grow and form a solid mass within or attached to the kidney. Because the kidneys are made up of several types of cells, there are several types of kidney tumors.
Renal Cell Carcinoma
The American Cancer Society reports that the most common type of kidney tumor is renal cell carcinoma, which accounts for 90 percent of all types of kidney cancer. Renal cell carcinoma usually forms one tumor in one part of the kidney but occasionally can form several tumors in one kidney or form tumors in both kidneys. There are several subtypes of renal cell carcinoma, which are defined based on how the cells look when magnified with a microscope. Some types of renal cell carcinoma are clear renal cell carcinoma, in which the cells look clear under the microscope; papillary renal cell carcinoma, in which the tumors make finger-like projections; collecting duct renal cell carcinoma, a rare type of kidney cancer in which cells of the tumor form irregular tubes. The most common symptom of renal cell carcinoma is blood in the urine. Back pain where the kidneys are located may also occur.
Transitional Cell Carcinoma
According to the National Cancer Institute, another type of kidney tumor is transitional cell carcinoma, which affects the renal pelvis. A tube called a ureter brings urine from the kidney to the bladder, and the renal pelvis is the region where the ureter attaches to the kidney. The American Cancer Society adds that transitional cell carcinoma cells look much like bladder cancer under the microscope. The symptoms of this type of cancer, similar to renal cell carcinoma, include blood in the urine and occasionally back pain. People with transitional cell carcinoma often have a good prognosis, and 9 out of 10 people with this disease are successfully treated if the tumor is found early enough.
Wilms' Tumor
Merck Manuals, an online medical library, reports that Wilms' tumor, also called nephroblastoma, usually develops in children younger than 5 years old. It can even develop in utero or in newborns, though this rarely occurs. The specific cause of this type of kidney tumor is not known, but scientists think that genes inherited from the parents play a role. The first symptom of Wilms' tumor is usually a painless lump in the abdomen; when the cancer progresses, the whole abdomen may become larger, and the child may experience abdominal pain, a decreased appetite, nausea and vomiting. Blood may also appear in the urine.
