Spread or “metastasis”
of tumor cells to bone is a common problem
in cancer patients. Bone is the third most
common site of tumor spread, behind only liver
and lung. Each year, about 100,000 bone metastases
are reported in the United States, with bone
metastases most commonly occurring in patients
with breast, prostate, lung and kidney cancer.
When tumor cells enter the blood stream and
subsequently pass into the marrow of the bone,
they begin to multiply and grow. This growing
tumor destroys the bone around it and invades
nerve fibers in and around the bone. If untreated,
bone can become weakened and potentially fracture.
Pain can become severe and even disabling,
requiring large doses of narcotic medications
to control. Bone metastases that are at risk
of fracture, particularly the bones of the
legs, may be treated surgically, often with
placement of a metal rod to stabilize the
bone. External radiation is currently the
standard of care in patients with bone pain.
Radiation results in reduction in pain for
a majority of patients. However, this can
take 4-6 weeks to improve symptoms and about
20-30% of patients with bone pain will not
respond to radiation therapy. Some patients
who have recurrent pain at sites of previous
radiation therapy cannot be retreated with
radiation due to dose limitations of radiation
treatment.
Image-guided interventional radiologic treatment
of bone tumor has rapidly evolved and proven
effective in treatment of certain metastatic
bone tumors. This treatment has been seen
to be particularly well suited to patients
with only one or a few metastatic lesions,
especially if these lesions are locally destroying
bone (lytic), often seen in lung and kidney
tumors. Interventional treatment is more difficult
and typically not utilized in more dense (blastic)
metastatic tumors, typically seen with prostate
and breast cancers.
Procedures commonly utilized by the interventional
radiologist in the treatment of metastatic
bony tumor include embolization, radiofrequency
ablation, and methacrylate injection.
Embolization is utilized
to decrease blood flow to tumor. It may be
used prior to surgical removal of tumor to
greatly decrease blood loss during surgery.
It may also be used in combination with radiofrequency
ablation of tumor. During the embolization
procedure, a tiny plastic catheter is advanced
into the artery at the top of one leg and
is then guided under x-ray visualization into
the vessel supplying the particular bone and
the bone tumor. This small catheter is advanced
into the vessel as close to the tumor as possible
and very tiny plastic particles are then injected
to block the blood vessels going to the tumor.
When used in combination with radiofrequency
ablation of tumor, this decreased blood flow
helps to promote cell death during the ablation
procedure.
Radiofrequency Ablation
Radiofrequency ablation
(RFA) is a rapidly growing technology that
can be very effective in appropriate cases
of metastatic tumor. A needle is guided through
the skin using CAT scan guidance with the
tip of the needle placed into the tumor. An
electric current is then administered through
the needle, causing heating of the cells around
the needle and resulting in tumor death. The
needle is then removed and a small bandage
applied. The procedure usually takes about
30 minutes to treat a single lesion, and several
lesions can be treated in a single session
if necessary. In one multicenter study, 59/62
patients (95%) experienced a clinically significant
drop in their pain level and required less
medication to control pain.
Methacrylate Injection
When there is concern about
possible fracture through a lesion following
ablation, methacrylate injection (osteoplasty)
may be utilized. Methacrylate is a glue-like
cement, acting to replace destroyed bone in
area of metastatic tumor. The cement can be
injected through the needle used to guide
the RFA probe into place, prior to its removal.
The methacrylate may also have the effect
of killing some nerve fibers in the area of
destroyed bone, augmenting pain relief.
As with all tumors, close follow-up is needed
after interventional treatment. Additional
lesions may be able to be treated with repeat
intervention, if appropriate.
Treatment of Benign
Tumors
While effective in treating
cancerous tumors to bone, RFA can also be
useful in treatment of some benign, non-cancerous
lesions of bone. One particular benign lesion,
osteoid osteoma, responds particularly well
to RFA, rapidly relieving pain which can be
very problematic with this particular entity.
