Kidney Cancer (Renal Cell)
Kidney cancer occurs when cells in either the cortex of the kidney or cells in the renal pelvis grow uncontrollably and form tumors that can invade normal tissues and spread to other parts of the body.
Cancers are described by the types of cells from which they arise. Again, when discussing kidney cancer, the cortex and the renal pelvis must be mentioned separately. In the kidney cortex, the vast majority of cancers arise from the cells that line the collecting tubules, more specifically, the proximal tubules. Cancers that develop from lining such as this are called carcinomas. In this case, they are obviously called renal cell carcinomas. Over 75% of renal cell carcinomas are called clear cell carcinomas, named after the characteristics they display when looking at them under the microscope. Other classifications, in decreasing order of prevalence, include chromophilic, chromophobic, oncocytic, and collecting duct cancers. However, it does not appear that these various types of renal cell carcinoma differ in presentation or prognosis.
Cancers of the renal pelvis, or medulla, are uncommon. Over 90% of cancers that develop in the renal pelvis are called transitional cell carcinomas. They are so named because they develop from cells that line the renal pelvis and upper ureters.
How is kidney cancer diagnosed and staged?
Work up of a kidney cancer usually starts after the patient presents with symptoms, with the exception of those cancers that are found incidentally. The entire point of all of the tests done prior to treatment of kidney cancer is to determine the extent of disease that is present so that treatment can be adjusted accordingly. This includes documenting the extent of disease both locally, in the tissues and lymph nodes surrounding the kidney, as well as ensuring there is no spread distantly, outside the area of the kidney (called metastases). The most sensitive test to document local disease is the CT scan, which has been shown to predict the tumor extent preoperatively in 90% of patients. MRI scans have been used to ensure the tumor has not involved any of the large blood vessels that are in the vicinity of the kidney. Other tests, including basic laboratory blood tests and analysis of the urine. In addition, a chest x-ray and bone scan are usually done, to ensure against metastatic spread to the lungs and bones, respectively. In the case of cancers within the inner part of the kidney (the collecting system), the IVP is an additional test that is extremely important to not only document the local extent of tumor, but also to ensure against simultaneous tumors somewhere else in the urine collecting system.
To obtain a diagnosis of any cancer, tissue or cells must be examined by a pathologist. Therefore, to obtain a diagnosis of kidney cancer, a biopsy is often obtained by inserting a needle into the presumed tumor mass during a CT scan. However, there are also times that the CT scan and/or MRI is so convincing that the mass is a tumor, that the initial biopsy is done during an open surgical procedure, which is done to ultimately remove the kidney, as treatment for the kidney cancer. This, obviously, must be determined on an individual basis.
After all of these tests are performed, the stage of the cancer is known. The staging of a cancer basically describes how much it is grown before the diagnosis has been made, documenting the extent of disease. This is often extremely important in terms of what treatment is offered to each individual patient. Before the staging systems are introduced, first some background on how cancers grow and spread, and therefore advance in stage.
Cancers cause problems because they spread and can disrupt the functioning of normal organs. One way kidney cancer can spread is by local extension to invade through the normal structures. This initially includes the kidney, hence giving the symptoms of hematuria, a mass and abdominal pain. If more growth occurs, it could grow to involve the main vein that leaves the kidney (the renal vein), the large vein that returns blood from the bottom half of the body to the heart (the inferior vena cava), or into other organs-most commonly the adrenal glands.
Kidney cancer can also spread by accessing the lymphatic system. The lymphatic circulation is a complete circulation system in the body (somewhat like the blood circulatory system) that drains into various lymph nodes. When cancer cells access this lymphatic circulation, they can travel to lymph nodes and start new sites of cancer. This is called lymphatic spread. Kidney cancer can spread, at times, into the lymph nodes surrounding the kidney, called the perirenal lymph nodes.
Kidney cancers can also spread through the bloodstream. Cancer cells gain access to distant organs via the bloodstream and the tumors that arise from cells' travel to other organs are called metastases. Cancers of the kidney generally spread locally into the fat surrounding the kidney, the adrenal glands, or the veins prior to spreading via the lymphatic system or the bloodstream. However, tumors, especially larger tumors, can access the bloodstream and spread to the lungs and bones, most commonly. Kidney tumors have also been known to spread to the testes and ovaries through the testicular or ovarian veins that are in close proximity to the kidney.
The staging system used today in kidney cancer is designed to describe the extent of disease within the area of the kidney, in the surrounding lymph nodes, and distantly. The staging system most commonly used today to describe kidney tumors is the "TNM system", as described by the American Joint Committee on Cancer. This replaced the "Robson Modification of the Flocks and Kadesky Staging System" because of its superiority in describing the local extent and lymph node involvement. The TNM systems are used to describe many types of cancers. They have three components: T-describing the extent of the "primary" tumor (the tumor in the kidney itself); N-describing the spread to the lymph nodes; M-describing the spread to other organs or structures (i.e.-metastases).
The "T" stage is as follows:
For kidney (cortex) tumors:
- T1-tumor size of 7 cm or less and confined to the kidney
- T2-tumor size more than 7 cm, but still confined to the kidney
- T3a-tumor invading into the adrenal gland or just outside of the kidney
- T3b-tumor invading into the renal vein or inferior vena cava, but contained below the diaphragm
- T3c- tumor invading into the renal vein or inferior vena cava, but extending above the diaphragm
- T4-tumor invades outside of these areas
For collecting system tumors:
- T1-tumor contained within the collecting system
- T2-tumor invades into the muscular layer of the wall of the collecting system
- T3-tumor invades into the fat surrounding the collecting system
- T4-tumor invades into other organs
The "N" stage is as follows for any subsite:
- N0-no spread to lymph nodes
- N1-tumor spread to a single lymph node
- N2-tumor spread to multiple lymph nodes or for collecting system tumors, lymph node spread that is between 2 and 5 cm
- N3-for collecting system tumors only, those lymph nodes that are >5 cm
The "M" stage is as follows:
- M0-no tumor spread to other organs
- M1-tumor spread to other organs
The overall stage is based on a combination of these T, N, and M parameters:
For kidney cortex tumors
- Stage I: T1N0M0
- Stage II: T2N0M0
- Stage III:
- Stage IV: and T4, any N2 or M1
For collecting system tumors
- Stage I: T1N0M0
- Stage II: T2N0M0
- Stage III: T3N0M0
- Stage IV: any T4, any N1-3, any M1
Though complicated, these staging systems help physicians determine the extent of the cancer, and therefore make treatment decisions regarding a patient's cancer.