A biopsy is the process of taking a small sample of tissue from a body structure. While the tissue biopsy can be done in a number of ways, a special needle is usually used that, when deployed, takes a small “core” or piece of tissue out of the body. The needle can be placed into the body in a number of different ways. For kidney biopsies, the needle is usually placed through the skin of the back. The needle is guided by some type of radiologic imaging study which may be an ultrasound, CT scan or other imaging modality.

Biopsies of kidney masses to check for the presence of kidney cancer are rarely performed. Kidney biopsy is not suggested for two reasons. First, there is a small chance that by taking a biopsy the cancerous tissue in the kidney may be spread. Under normal conditions, kidney cancer can be controlled locally by the body by maintaining the cancer in limited spaces. The capsule of the kidney, the fat around the kidney, and the leathery layer that surrounds the kidney, which is known as Gerota’s fascia, all may help to contain a kidney cancer. Putting the biopsy needle through all of these tissues and into the cancer presents a small risk of spreading the cancer cells outside of these natural barriers. While the risk of spreading the cancer cells with a biopsy is very small, there is a significantly poorer outcome that can be expected if the cancer has been spread.

The second reason that doctors generally prefer not to biopsy the kidney is that the biopsy has approximately a 20% chance of being a “false negative” (cancer is present but is missed by the biopsy). This means that while the small piece of tissue that has been removed may not show any cancer, the biopsy may have missed the target lesion or may have missed a cancer within the target lesion. Therefore, a negative biopsy can be misleading and may hurt the chances of cure in the long term.

Copyright 2006 Kidney Cancer Institute