Kidney tumours are classified according to their stage, subtype, and the grade of aggressiveness of the tumour cells. These three elements are the basis for your possible treatment pathway.
Tumour stage indicates how advanced the tumour is and whether or not there are metastases in the lymph nodes or other organs.
Kidney tumour stage is based on the Tumour Node Metastasis (TNM) classification. The urologist looks at the size and invasiveness of the tumour (T) and determines how advanced it is, based on 4 stages. Whether any lymph nodes are affected (N) or if the cancer has spread to any other parts of your body (M) is also checked. If kidney tumours metastasise they generally spread to the lungs, or to the bones or brain. Figures 1 to 5 illustrate the different stages.
Next to staging, the subtype of kidney tumours is important. The subtype is determined by a pathologist and the procedure is known as histopathological analysis. The specialist examines the tumour tissue either taken during a biopsy or after it has been removed during surgery. Renal biopsy is not a standard procedure in the diagnosis of kidney cancer. In most cases, the subtype of your tumour will not be known until after you have surgery.
There are various subtypes of kidney tumours. Most kidney tumours are renal cell carcinomas. Of these, the most common subtype is clear cell renal cell carcinoma
If you are diagnosed with a rare kidney tumour your doctor will give you detailed information about different treatment possibilities. These may differ from therapy for the more common kidney cancer subtypes. Treatment options are discussed by a multidisciplinary team of doctors, to find the best approach for you (See: The medical team).
Some tumours in the kidney are non-cancerous. These are known as benign kidney tumours. The most common benign tumours of the kidney are oncocytomas and angiomyolipomas.
Oncocytomas are generally diagnosed after histopathological analysis, because scans cannot always identify them clearly. The most common treatment options for these tumours are partial nephrectomy and active surveillance. Read more about these treatment options in the section Localised Kidney Cancer.
An angiomyolipomas (AML) is a benign tumour and more likely to occur in women. It is generally diagnosed after ultrasound, CT or MRI scans, or if the tumour bleeds and causes symptoms. Although AML is a benign tumour, the risk of spontaneous bleeding in the kidney increases if it continues to grow. Surgery to remove the tumour is recommended if:
- You have a large AML (a tumour larger than 4 cm)
- You are a woman under the age of 45
- The tumour causes symptoms
- It is difficult for you to visit your doctor in case of emergency, because you live far away from a hospital or you have limited mobility.
Generally, an AML is removed with partial nephrectomy but in some cases it may be necessary to remove the whole kidney. Radical nephrectomy is recommended in case of severe bleeding of the tumour.
Some masses in the kidney are not tumours but renal cysts. These are sacs filled with fluid located on the kidney and are easily recognised on a CT scan. Cysts can be malignant. If this is the case they need to be removed by surgery.
The third component of the classification is an evaluation of how aggressive the tumour cells are. The Fuhrman nuclear grade is the most commonly used system to determine this. The pathologist classifies your tumour in 1 of 4 grades.
After diagnosis and classification, your doctor will discuss different treatment and follow-up options with you. The recommended treatment pathway is based on the TNM staging, the Fuhrman grade, and the subtype of the tumour. Your individual prognosis can also be estimated after classification. However, keep in mind that this is a prediction which does not take into account any unexpected developments.