There are 2 main types of primary kidney cancer. They are renal cortical tumors (renal cell cancer, or RCC) and upper tract urothelial tumors (transitional cell tumors). They are different in how they develop and change over time and in how they are treated.
Renal Cortical Tumors
More than 90 percent of kidney tumors are renal cortical tumors. They start in the main part of your kidney, which has structures called renal tubules.
There are many kinds of renal cortical tumors. They don’t all behave the same. The treatment you receive — including medications, imaging tests, and whether you need surgery — depends on the type of tumor you have.
Most types of kidney tumors are malignant (cancerous). However, some tumors are benign (not cancer). They usually don’t cause symptoms unless they grow to be very large. These benign tumors can’t spread to other parts of the body. They usually are removed through surgery and don’t come back. Examples of benign tumors include renal cysts, oncocytomas, and angiomyolipomas.
Clear cell renal cell carcinoma (clear cell RCC)
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 renal cell carcinoma (papillary 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 renal cell carcinoma (chromophobe RCC)
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.
Collecting duct tumors and renal medullary cancer
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 renal cell carcinoma (unclassified RCC)
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.
Upper Tract Urothelial Tumors
This type of kidney cancer starts in your renal pelvis. That’s where urine collects before it goes into the ureter, a tube that connects the kidney to the bladder. Urothelial tumors affect the lining of the urinary tract, including the renal pelvis, ureters, bladder, and urethra. Urothelial (transitional cell) tumors are different from renal cortical tumors. They come from a different type of cell and behave more like bladder cancer.
The surgical strategy for these cancers is slightly different. To fight urothelial tumors that have spread, we use treatments developed for bladder cancer. Because of these differences, it is important to distinguish between renal cortical and upper tract urothelial tumors.