How is cancer diagnosed and staged?
Early
detection of cancer can greatly improve the odds of successful treatment and
survival. Physicians use information from symptoms and several other procedures
to diagnose cancer. Imaging techniques such as X-rays, CT scans, MRI scans, PET
scans, and ultrasound scans are used regularly in order to detect where a tumor
is located and what organs may be affected by it. Doctors may also conduct an
endoscopy, which is a procedure that uses a thin tube with a camera and light
at one end, to look for abnormalities inside the body.
Extracting
cancer cells and looking at them under a microscope is the only absolute way to
diagnose cancer. This procedure is called a biopsy. Other types of molecular
diagnostic tests are frequently employed as well. Physicians will analyze your
body's sugars, fats, proteins, and DNA at the molecular level. For example,
cancerous prostate cells release a higher level of a chemical called PSA
(prostate-specific antigen) into the bloodstream that can be detected by a
blood test. Molecular diagnostics, biopsies, and imaging techniques are all
used together to diagnose cancer.
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After
a diagnosis is made, doctors find out how far the cancer has spread and
determine the stage of the cancer. The stage determines which choices will be
available for treatment and informs prognoses. The most common cancer staging
method is called the TNM system. T (1-4) indicates the size and direct extent
of the primary tumor, N (0-3) indicates the degree to which the cancer has
spread to nearby lymph nodes, and M (0-1) indicates whether the cancer has
metastasized to other organs in the body. A small tumor that has not spread to
lymph nodes or distant organs may be staged as (T1, N0, M0), for example.
TNM
descriptions then lead to a simpler categorization of stages, from 0 to 4,
where lower numbers indicate that the cancer has spread less. While most Stage
1 tumors are curable, most Stage 4 tumors are inoperable or untreatable.
How is cancer treated?
Cancer
treatment depends on the type of cancer, the stage of the cancer (how much it
has spread), age, health status, and additional personal characteristics. There
is no single treatment for cancer, and patients often receive a combination of
therapies and palliative care. Treatments usually fall into one of the following
categories: surgery, radiation, chemotherapy, immunotherapy, hormone therapy,
or gene therapy.
Surgery
Surgery
is the oldest known treatment for cancer. If a cancer has not metastasized, it
is possible to completely cure a patient by surgically removing the cancer from
the body. This is often seen in the removal of the prostate or a breast or
testicle. After the disease has spread, however, it is nearly impossible to
remove all of the cancer cells. Surgery may also be instrumental in helping to
control symptoms such as bowel obstruction or spinal cord compression.
Radiation
Radiation
treatment, also known as radiotherapy, destroys cancer by focusing high-energy
rays on the cancer cells. This causes damage to the molecules that make up the
cancer cells and leads them to commit suicide. Radiotherapy utilizes
high-energy gamma-rays that are emitted from metals such as radium or
high-energy x-rays that are created in a special machine. Early radiation
treatments caused severe side-effects because the energy beams would damage
normal, healthy tissue, but technologies have improved so that beams can be
more accurately targeted. Radiotherapy is used as a standalone treatment to
shrink a tumor or destroy cancer cells (including those associated with leukemia
and lymphoma), and it is also used in combination with other cancer treatments.
Chemotherapy
Chemotherapy
utilizes chemicals that interfere with the cell division process - damaging
proteins or DNA - so that cancer cells will commit suicide. These treatments
target any rapidly dividing cells (not necessarily just cancer cells), but
normal cells usually can recover from any chemical-induced damage while cancer
cells cannot. Chemotherapy is generally used to treat cancer that has spread or
metastasized because the medicines travel throughout the entire body. It is a
necessary treatment for some forms of leukemia and lymphoma. Chemotherapy
treatment occurs in cycles so the body has time to heal between doses. However,
there are still common side effects such as hair loss, nausea, fatigue, and
vomiting. Combination therapies often include multiple types of chemotherapy or
chemotherapy combined with other treatment options.
Immunotherapy
Immunotherapy
aims to get the body's immune system to fight the tumor. Local immunotherapy
injects a treatment into an affected area, for example, to cause inflammation
that causes a tumor to shrink. Systemic immunotherapy treats the whole body by
administering an agent such as the protein interferon alpha that can shrink tumors.
Immunotherapy can also be considered non-specific if it improves
cancer-fighting abilities by stimulating the entire immune system, and it can
be considered targeted if the treatment specifically tells the immune system to
destroy cancer cells. These therapies are relatively young, but researchers
have had success with treatments that introduce antibodies to the body that
inhibit the growth of breast cancer cells. Bone marrow transplantation
(hematopoetic stem cell transplantation) can also be considered immunotherapy
because the donor's immune cells will often attack the tumor or cancer cells
that are present in the host.
Hormone therapy
Several
cancers have been linked to some types of hormones, most notably breast and
prostate cancer. Hormone therapy is designed to alter hormone production in the
body so that cancer cells stop growing or are killed completely. Breast cancer
hormone therapies often focus on reducing estrogen levels (a common drug for
this is tamoxifen) and prostate cancer hormone therapies often focus on
reducing testosterone levels. In addition, some leukemia and lymphoma cases can
be treated with the hormone cortisone.
Gene therapy
The
goal of gene therapy is to replace damaged genes with ones that work to address
a root cause of cancer: damage to DNA. For example, researchers are trying to
replace the damaged gene that signals cells to stop dividing (the p53 gene)
with a copy of a working gene. Other gene-based therapies focus on further
damaging cancer cell DNA to the point where the cell commits suicide. Gene
therapy is a very young field and has not yet resulted in any successful
treatments.
How can cancer be prevented?
Cancers
that are closely linked to certain behaviors are the easiest to prevent. For
example, choosing not to smoke tobacco or drink alcohol significantly lower the
risk of several types of cancer - most notably lung, throat, mouth, and liver
cancer. Even if you are a current tobacco user, quitting can still greatly
reduce your chances of getting cancer.
Skin
cancer can be prevented by staying in the shade, protecting yourself with a hat
and shirt when in the sun, and using sunscreen. Diet is also an important part
of cancer prevention since what we eat has been linked to the disease.
Physicians recommend diets that are low in fat and rich in fresh fruits and
vegetables and whole grains.
Certain
vaccinations have been associated with the prevention of some cancers. For
example, many women receive a vaccination for the human papillomavirus because
of the virus's relationship with cervical cancer. Hepatitis B vaccines prevent
the hepatitis B virus, which can cause liver cancer.
Some
cancer prevention is based on systematic screening in order to detect small
irregularities or tumors as early as possible even if there are no clear
symptoms present. Breast self-examination, mammograms, testicular
self-examination, and Pap smears are common screening methods for various
cancers.
Development of gene therapyBack to top
Some
types of gene therapy have been tested on cells in a test tube. These are now
being given to small groups of patients in clinical trials. Clinical trials are carried out to find new
and better ways of treating cancer. If a drug has been tested in a laboratory
and seems to be helpful, it's then tested on patients. This is the first stage
of a trial. The aim is to find a safe dose of the drug and see what side
effects it may cause.
Gene
therapy is very new. For this reason, doctors and other medical staff carry out
frequent and careful checks on every patient who is having one of these
treatments.
If
you are having gene therapy, your doctor will explain the treatment, the
procedures being used and how you'll be looked after while you're taking it.
You can ask your doctor or nurse for information and advice if you have
concerns at any time.
Our
bodies are made up of millions of tiny cells. Inside each cell is an area
called the nucleus, which contains 23 pairs of chromosomes. Chromosomes are
made up of thousands of genes. Genes are tiny chemical structures. They carry
the instructions that tell cells how to work, and they control our growth and
development. They determine what we look like and how our bodies work. They
also organise the repair of damaged cells and tissues.
Chromosomes, genes and
DNA
We
have at least 30,000 different genes. Each of us has two copies of every gene.
One set of copies is inherited from our mother, the other from our father. They
are made up of a chemical called DNA (deoxyribonucleic acid). DNA controls all
of the processes in our bodies by producing proteins that carry out
the genes’ instructions.
When
genes are damaged they may cause the production of abnormal proteins that lead
to disease. Changes in particular genes can cause cancer to develop.
The
cells in many tissues in our bodies are constantly dividing to make new cells that
replace those that are damaged or worn out. This process is controlled by
particular genes. They make sure that exactly the right number and type of new
cells are made to meet our needs.
If
a gene is damaged, cells may start to divide in an uncontrolled way. This may
eventually lead to a cancer. The damage to the genes is called a
mutation.
As
we learn more about genes and cancer, it seems likely that almost all cancers
might be caused by faulty or damaged genes.
It's
likely that several changes or mutations have to happen in the genes before a
cell starts to divide abnormally and multiply out of control. This series of
changes may be brought about by various factors, including cigarette smoking,
environmental factors or other causes that we are not yet aware of.
The
faulty genes may lead to cancer in the following ways:
·
The damaged gene can
trigger cancerous changes in the cells. Some genes that can do this have been
identified and are called oncogenes.
·
Some genes reduce the
risk of a cancer developing by repairing damage to other genes. These are
called tumour-suppressor genes. If tumour-suppressor genes are damaged or
mutated so that they don't work, this may allow a cancer to develop.
Gene
therapy means putting genetic material (DNA) into cells so they can make
proteins that they don't usually make. These proteins will help fight disease.
Research has shown the following:
·
Single genes can be
taken from human cells and grown (cloned) in the laboratory, outside the body.
·
These cloned genes can
be altered to make them work differently.
·
The altered genes can
be put back into cells living in the body. This is usually done by inserting
the gene into particular chemicals (liposomes) or cells (such as viruses that
have been treated so that they are no longer harmful). The protein or cell used
to deliver the altered gene into the body is known as a vector.
Sometimes,
the genes themselves are introduced directly into the tissues. These are called
naked genes.
Gene
therapy may be used to treat cancer in the following ways:
·
Genes can be put into
the cancer cells to make them more sensitive to treatments such as chemotherapy.
·
Genes may be put into
cancer cells and then activated to produce a poisonous substance (toxin) that
kills the cell.
·
Genes can be put into
cancer cells which make those cells more obvious to the body's own defences
(the immune system), so that they are destroyed 'naturally' by the cells of our
immune system.
·
Damaged genes may be
replaced by the version that works correctly.
·
New genes may be put
into normal cells to make them more resistant to the side effects of treatments
such as radiotherapy and chemotherapy. This protects the normal
cells from the treatments so that higher doses can be given. At present the
risk of damage to normal cells often limits the doses that can be used.
Research
is now going on into all the above types of gene therapy.
As
this is still an experimental treatment, the way in which gene therapy is given
may vary or change as new techniques develop.
Initially,
cells are taken from a blood sample. The genes are isolated and changed
(engineered) in the laboratory. They are then attached to a chemical or
inserted into a cell. This acts as a carrier.
At
present, the changed genes within the carrier are usually given by a drip into
a vein (intravenously) through a small tube (cannula) inserted into the vein.
They may be given directly into the tumour by injection.
Gene
therapy is a new technique that is being developed for the treatment of a
number of different cancers. At the moment it is experimental and it will take
many years to find out if it can have an important role in the treatment of
cancer.
Many
clinical trials are taking place, using a variety of different gene therapies
for many different types of cancer. Nearly all of these studies are at a very
early stage. Again, it will be many months or even years before the results are
known.
Some
studies have finished. Most of these looked at the safety of gene therapy.
These have shown that introducing new genes into both tumour cells and normal
cells in patients is possible. There have been very few side effects with the
gene-based treatments used so far, which is encouraging for the future.
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