Clear cell carcinomas are the most common type of kidney cancer. They are also the most responsive to treatment with medication. Systemic therapy is when a medical oncologist (cancer doctor) gives you medications. These drugs will spread in your body through your blood to treat cancer cells wherever they are. Clear cell carcinomas make up about 90 percent of kidney cancers that are metastatic (have spread) to other body parts. They make up about 70 percent of cancerous kidney tumors overall.

Some are aggressive. Others are called indolent, which means they grow slowly. Clear cell tumors can leave the kidney and metastasize (spread) to other parts of the body.

Pathologists review the shape and other features of the cancer cells under a microscope. They give the cells a grade. They give a higher grade to cells that look like they are more aggressive. High-grade tumors are more likely to come back after surgery. They also have a higher risk of spreading to other parts of the body.

Clear cell RCC has been studied the most because it is by far the most common kidney cancer. Most of the medications we use to treat kidney cancer were developed to treat clear cell RCC.

Papillary tumors make up 10 to 15 percent of kidney tumors. There are different types of papillary tumors. The kinds studied the most are called type 1 and type 2 papillary RCC. Type 1 usually grows slowly, but there often are several tumors in 1 or both kidneys. Type 2 tumors tend to be more aggressive. It’s harder to predict how they will behave. Other kinds of papillary RCC may not fit into either of these categories.

Papillary tumors can be associated with certain syndromes that are inherited. These types of tumors include hereditary papillary renal carcinoma, hereditary leiomyomatosis, and renal cell carcinoma. Hereditary cancer is caused by a gene mutation (change). It can be passed down through the genes to generations of a family. When we say family, we mean people related to you by blood. They are not related to you through marriage or adoption.

If your doctor thinks you have one of these syndromes, you may need genetic testing. This is important if your cancer started at a very young age or if blood relatives had the same cancer.

Chromophobe tumors make up about 5 percent of kidney tumors. In many people, they are less aggressive. But they can spread just like other types of RCC.

Oncocytoma is a benign (not cancer) tumor. About 5 to 10 percent of kidney tumors are oncocytomas. People who have larger oncocytomas may have surgery to remove them. This lowers the risk of complications, such as pain and bleeding in the kidney.

These are very rare and make up less than 1 percent of kidney tumors. They are more common in younger adults. They are highly aggressive cancers that spread from the kidney early. Once they have spread, they need different types of systemic therapy than other kidney cancers.

Unclassified tumors don’t easily fit into the other categories. They look different from other tumors under a microscope. These cancers are often aggressive. Although they are rare, they make up 3 to 5 percent of kidney tumors.