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Renal carcinoma, also called renal cell carcinoma (RCC), renal adenocarcenoma, or hypernephroma, is a malignant cancer that originates in the proximal convoluted tubule in the nephron of the kidney. There are five types of renal carcinoma, classified by distinct characteristics of the cancerous tissue. The five types are clear cell renal cell carcinoma, papillary renal carcinoma, chromophobe renal cell carcinoma, collecting duct, and unclassified renal carcinoma.
The term renal refers to the kidney, a paired organ located in the posterior, or back, abdomen. The kidney is responsible for several functions, including production of urine, controlling blood pressure and volume, filtering out unneeded material from the blood, and reabsorbing needed sodium, water, and sugars into the bloodstream. The nephron is the functional unit within the kidney and the proximal tubule is a structure within the nephron. Carcinoma is a type of cancer that affects epithelial cells, in this case the epithelial cells lining the proximal convoluted tubule. Renal carcinoma usually exhibits few symptoms and is very difficult to control once it has metastasized, or spread.
Clear cell renal cell carcinoma is the most common type of renal carcinoma. It is named thus because the cancerous cells in such cases appear clear or very light under a microscope. Sometimes patients with clear cell carcinoma will exhibit characteristics of other types, especially granular and papillary.
Papillary renal carcinoma, also called chromophilic RCC, is differentiated by the finger-shaped projections called papillae that extend from the cancerous cells. There are two subtypes of papillary RCC, type I and type II. Type I is more common in general, but type II is more common amongst patients whose renal carcinoma has metastasized. This indicates that the prognosis, or the doctor’s prediction of the patient’s chances, is better for type I papillary RCC than for type II.
Chromophobe renal carcinoma cells appear very similar to clear cell carcinoma under a microscope, except that they might be larger. Doctors will use other characteristics, such as a positive colloidal iron stain, to differentiate this type of RCC. Chromophobe RCC usually has less chance of metastasizing than clear cell, and so yields a better prognosis. When it does metastasize, it often moves to the liver, so this is an important area to watch.
Collecting duct carcinoma (CDC), also called Bellini duct tumor, is a very rare and very aggressive type of renal carcinoma. Under a microscope, CDC appears very similar to papillary renal carcinoma. Because it is so rare, little is known on how to best treat CDC, outside of surgery. Also uncommon is the unclassified group of renal carcinomas, which do not fit the classifications of any of the aforementioned types. These irregular tumors are often aggressive and do not respond to traditional treatment methods, besides surgery.
If the tumor is localized in the kidney and the patient can withstand it, doctors recommend surgery as the best chance of curing the cancer. In a procedure called a nephrectomy, the doctor removes a part or all of the kidney, and sometimes the surrounding tissue and bladder as well. If the cancer has metastasized, renal carcinoma is very difficult to control. Interleuken-2 (IL-2) therapy is effective for some patients, but it is also very toxic, so it can only be used on patients who are otherwise very healthy. Some kinase inhibitor drugs and hormone treatments have been effective at reducing the growth of tumors.