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.