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What is targeted therapy?
Targeted therapies can be used to treat different kinds of
diseases. Here we will focus on their use to treat cancer. Some of the
cancers that may be treated with targeted therapy include certain types
of lung, pancreatic, head and neck, liver, colorectal, breast, and
kidney cancers.
Targeted therapy is a new type of cancer treatment that uses
drugs or other substances to identify and attack cancer cells while
doing little damage to normal cells. These therapies attack the cancer
cells' inner workings -- the programming that makes them different from
normal, healthy cells. Each type of targeted therapy works differently,
but all alter the way a cancer cell grows, divides, repairs itself, or
interacts with other cells.
Targeted therapies are a major focus of cancer research today.
Many future advances against cancer will likely come from this field.
This document explains:
- the different ways that targeted therapy can work
- some of the types of targeted therapy
- how targeted therapies may change cancer treatment in the
future
How does targeted therapy work?
Targeted therapies are used to keep cancer from growing and
spreading. Normal cells must go through a process to become cancer
cells and to be able to grow into tumors. (This process is called carcinogenesis.)
Scientists have learned a lot about the molecules that are part of this
process and the signals a cell gets to keep this process going.
Targeted therapies disrupt this process. These drugs target
certain parts of the cellular changes and signals that are needed for a
cancer to develop and keep growing. These drugs are often grouped by
how they work, or what part of the cell they target.
Enzyme inhibitors
When most people think of enzymes, the first ones that come to
mind are the digestive enzymes that break down the food we eat. But
there are many other kinds of enzymes in our bodies, and they play a
key role in controlling nearly everything our cells do. Some targeted
therapies block certain proteins, or enzymes, that are signals for
cancer cells to grow. Blocking these signals can keep the cancer from
getting bigger and spreading. So even if the tumor is not getting
smaller, its out-of-control growth has been changed. This may give
regular chemotherapy (chemo) a better chance to work. The change in out
of control growth may also help people live longer, even without adding
other drugs. These drugs may be called small-molecule drugs,
signal-transduction inhibitors, or enzyme-inhibitors.
Apoptosis-inducing drugs
Some targeted therapies change proteins within the cancer
cells and cause the cells to die. These are called apoptosis-inducing
drugs. (Apoptosis
is the medical word for cell death. These drugs cause, or induce cell
death.) Many cancer treatments (including radiation and chemotherapy)
cause cell changes that lead to apoptosis. But targeted drugs in this
group are different, because they are aimed right at the parts of the
cell that control cell survival and death.
Angiogenesis inhibitors
Cancer cells need to form and be fed by new, healthy blood
vessels that come from nearby healthy, tissue. The process of forming
these blood vessels is called angiogenesis. Angiogenesis inhibitors are
targeted therapies that stop (or inhibit) this process. Angiogenesis
inhibitors stop the blood supply to tumors so they can't grow.
Many of these drugs work by blocking vascular endothelial
growth factor (VEGF). VEGF is a family of protein growth factors made
by some tumors. These VEGF proteins can attach to the VEGF receptors of
blood vessel cells. This causes new blood vessels to form around the
tumors. Blocking this process prevents angiogenesis, which would form
new blood vessels that would feed tumor growth.
How is targeted therapy used?
Targeted cancer therapies do not damage bone marrow or blood
cells like most standard chemo drugs do. They can be used alone or
along with other drugs. Many are used with other cancer treatments,
such as radiation or chemo. (This is called combination therapy.)
They often help to boost the effects of the main treatment. At this
time, targeted therapies are most often used along with other chemo
drugs.
Targeted therapy is still relatively new compared to other
forms of cancer treatment, like surgery, radiation, or regular chemo.
It is only within the last 10 years or so that it has proven useful as
a form of cancer treatment. And even though they mainly target the
cancer cells, these drugs are not perfect -- they can cause side
effects and sometimes serious reactions.
Types of targeted therapy in use today
Today there are many different types targeted therapies used
to treat cancer. Looking at examples helps to understand how these
drugs work. A few of the more commonly used targeted therapies are
listed here, but this is not a complete list. There are many different
targeted therapies in use and new ones are coming out all the time.
Some examples of small molecule targeted
therapies
Gleevec® (imatinib mesylate)
This is one of the first targeted therapies used to treat
cancer. It is used to treat gastrointestinal stromal tumor (or GIST, a
rare cancer of the gastrointestinal tract) and certain kinds of
leukemia. Gleevec targets abnormal proteins, or enzymes, that form on
and inside cancer cells and promote uncontrolled growth.
Iressa® (gefitinib)
Iressa is used to treat advanced non-small cell lung cancer.
This drug targets the epidermal growth factor receptor (EGFR). This
receptor is found on the surface of many normal cells, but on certain
cancer cells there are many more copies. EGFR takes in the signal
telling the cell to grow and divide. When Iressa blocks this signal, it
can slow or stop cell growth.
Sutent® (sunitinib)
This enzyme-inhibitor is used to treat advanced kidney cancer
and some gastrointestinal stromal tumors (or GIST, a rare cancer of the
gastrointestinal tract). It is a type of VEGF receptor inhibitor that
blocks an enzyme called tyrosine kinase. By doing this it keeps tumors
from making their own blood vessels to help them grow and spread.
Velcade® (bortezomib)
This enzyme-inhibitor may be used to treat multiple myeloma
that does not respond to other treatments. Velcade is a proteasome
inhibitor. A proteasome is a complex of enzymes that helps destroy
proteins that the cell no longer needs. Some of these proteins help to
regulate cell function and growth. Velcade stops the proteasome from
breaking down these proteins, which in turn causes the cancer cells to
die
Other drug that may be called targeted
therapies
There are other cancer treatments that are included in the
group of drugs called targeted therapies. Some examples of these are:
- Monoclonal
antibodies, such as
- Campath® (alemtuzumab)
- Erbitux® (cetuximab)
- Mylotarg® (gemtuzumab ozogamicin)
- Rituxan® (rituximab)
- Herceptin® (trastuzumab)
- Avastin® (bevacizumab)
- Interleukins
- Interferons
- Granulocyte-macrophage colony-stimulating factor
The targeted therapies listed above are often grouped as
immunotherapies,
or treatments that work with your immune system to
fight cancer. But some of them also act as angiogenesis inhibitors
(bevacizumab) or enzyme inhibitors (cetuximab and trastuzumab). You can
learn more about these treatments in our documents, Immunotherapy
and
Gene Therapy.
How targeted therapies may change cancer
treatment in the future
Targeted cancer therapies are a huge part of cancer research
today. They are hoped to be a better way to treat cancer. Some doctors
think that in the future these treatments may be able to be custom-made
for each patient based on the molecular targets made by the patient's
tumor. Targeted cancer therapies are designed to kill cancer cells with
little damage to normal, healthy cells. This means less side effects
and better quality of life.
Most cells have had more than one step of the normal growth
process altered as they've become cancer. Researchers are looking at
ways to use different targeted therapies in combination to target more
of these pathways. Some cancer cells become resistant to these
therapies, too, and combinations of treatment may help prevent this.
Researchers are also looking for better ways to use targeted therapy
along with chemo and radiation to treat cancer.
Researchers are also looking at which cancers are best treated
with targeted therapies and when treatment should start. Targeted
therapies have helped many people with cancer, but this type of
treatment only helps some of the people who receive it. Researchers are
looking for ways to predict which patients will be helped the most, so
that only the patients who will benefit will be treated. At this time,
most targeted therapies are used to treat advanced cancers. Studies are
also being done to figure out the best ways to manage the side effects
of these treatments.
Researchers have made important progress in this field in
recent years. Newer, more effective treatments are now being tested
that will have a greater impact on the outlook for people with cancer
in the future.
Additional resources
More information from your American Cancer
Society
We have selected some related information that may also be
helpful to you. You can find these on our Web site or order them from
our toll-free number, 1-800-ACS-2345 (1-800-227-2345).
Along with the above, the American Cancer Society has
information about many different types of cancer and how they are
treated.
National organizations and Web sites*
Along with the American Cancer Society, other sources of
information and support include:
National Cancer
Institute
Toll-free number: 1-800-4-CANCER 1-800-422-6237
Web site: www.cancer.gov
*Inclusion on
this list does not imply endorsement by the
American Cancer Society.
No matter who you are, we can help. Contact us anytime, day or
night, for cancer-related information and support. Call us at
1-800-ACS-2345
or visit www.cancer.org.
References
Kwak EL, Clark JW, Chabner B. Targeted Agents: The Rules of
Combination. Clin
Cancer Res. 2007;13:5232-5237.
Ma J, Waxman DJ. Combination of antiangiogenesis with
chemotherapy for more effective cancer treatment. Molecular Cancer
Therapeutics. 2008;7:3670-3684.
National Cancer Institute. Targeted Cancer Therapies:
Questions and Answers. Accessed at
www.cancer.gov/cancertopics/factsheet/Therapy/targeted on January 12,
2009.
Viele CS. Keys to Unlock Cancer: Targeted Therapy. Oncology
Nursing Forum. 2005;32: 935-940.
Last Medical Review: 03/16/2009
Last Revised: 03/16/2009
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