Apa itu Kanker? what is cancer?

What is cancer?  


Cancer begins in your cells, which are the building blocks of your body.
Normally, your body forms new cells as you need them, replacing old cells that
die. Sometimes this process goes wrong. New cells grow even when you don't need
them, and old cells don't die when they should. These extra cells can form a
mass called a tumor. Tumors can be benign or malignant. Benign tumors aren't
cancer while malignant ones are. Cells from malignant tumors can invade nearby
tissues. They can also break away and spread to other parts of the body.

Most cancers are named for where they start. For example, lung cancer starts in
the lung, and breast cancer starts in the breast. The spread of cancer from one
part of the body to another is called metastasis. Symptoms and treatment depend
on the cancer type and how advanced it is. Treatment plans may include surgery,
radiation and/or chemotherapy.

What is cancer?

Cancer is a group of many related diseases that begin in cells, the body's
basic building blocks. To understand cancer, it is helpful to know what happens
when normal cells become cancerous.

The body is made up of many types of cells. Normally, cells grow and divide to
produce more cells as they are needed to keep the body healthy. Sometimes, this
orderly process goes wrong. New cells form when the body does not need them,
and old cells do not die when they should. The extra cells form a mass of
tissue called a growth or tumor. Not all tumors are cancerous; tumors can be
benign or malignant.

Benign tumors are not cancer. They can often be removed and, in most cases,
they do not come back. Cells in benign tumors do not spread to other parts of
the body. Most important, benign tumors are rarely a threat to life.

Malignant tumors are cancer. Cells in malignant tumors are abnormal and divide
without control or order. Cancer cells invade and destroy the tissue around
them. Cancer cells can also break away from a malignant tumor and enter the
bloodstream or lymphatic system.

Blood vessels include a network of arteries, capillaries, and veins through
which the blood circulates in the body. The lymphatic system carries lymph and
white blood cells through lymphatic vessels (thin tubes) to all the tissues of
the body. By moving through the bloodstream or lymphatic system, cancer can
spread from the primary (original) cancer site to form new tumors in other
organs. The spread of cancer is called metastasis.

What causes cancer?

Scientists have learned that cancer is caused by changes in genes that normally
control the growth and death of cells. Certain lifestyle and environmental
factors can change some normal genes into genes that allow the growth of
cancer. Many gene changes that lead to cancer are the result of tobacco use,
diet, exposure to ultraviolet (UV) radiation from the sun, or exposure to
carcinogens (cancer-causing substances) in the workplace or in the environment.
Some gene alterations are inherited (from one or both parents). However, having
an inherited gene alteration does not always mean that the person will develop
cancer; it only means that the chance of getting cancer is increased.
Scientists continue to examine the factors that may increase or decrease a
person's chance of developing cancer.

Although being infected with certain viruses, such as the human papillomavirus
(HPV), hepatitis B and C (HepB and HepC), and human immunodeficiency virus
(HIV), increases the risk of some types of cancer, cancer itself is not
contagious. A person cannot catch cancer from someone who has this disease.
Scientists also know that an injury or bruise does not cause cancer.

Can cancer be prevented?

Although there is no guaranteed way to prevent cancer, people can reduce their
risk (chance) of developing cancer by:

* not using tobacco products
* choosing foods with less fat and eating more vegetables, fruits, and
whole grains
* exercising regularly and maintaining a lean weight
* avoiding the harmful rays of the sun, using sunscreen, and wearing
clothing that protects the skin
* talking with a doctor about the possible benefits of drugs proven to
reduce the risk of certain cancers

Although many risk factors can be avoided, some, such as inherited conditions,
are unavoidable. Still, it is helpful to be aware of them. It is also important
to keep in mind that not everyone with a particular risk factor for cancer
actually gets the disease; in fact, most do not. People who have an increased
likelihood of developing cancer can help protect themselves by avoiding risk
factors (see Question 2) whenever possible and by getting regular checkups so
that, if cancer develops, it is likely to be found and treated early. Treatment
is often more effective when cancer is detected early. Screening exams, such as
sigmoidoscopy or the fecal occult blood test, mammography, and the Pap test,
can detect precancerous conditions (which can be treated before they turn into
cancer) and early-stage cancer.

The NCI is conducting many cancer prevention studies to explore ways to reduce
the risk of developing cancer. These studies are evaluating dietary
supplements, chemopreventive agents, nutrition, personal behaviors, and other
factors that may prevent cancer. More information about cancer prevention
trials is available in the following NCI resources:

See Question 6 for additional information about clinical trials related to the
prevention, screening, diagnosis, and treatment of cancer.

What are some of the common signs and symptoms of cancer?

Cancer can cause a variety of symptoms. Possible signs of cancer include the

* new thickening or lump in the breast or any other part of the body
* new mole or an obvious change in the appearance of an existing wart or
* a sore that does not heal
* nagging cough or hoarseness
* changes in bowel or bladder habits
* persistent indigestion or difficulty swallowing
* unexplained changes in weight
* unusual bleeding or discharge

When these or other symptoms occur, they are not always caused by cancer. They
can be caused by infections, benign tumors, or other problems. It is important
to see a doctor about any of these symptoms or about other physical changes.
Only a doctor can make a diagnosis. A person with these or other symptoms
should not wait to feel pain because early cancer usually does not cause pain.

If symptoms occur, the doctor may perform a physical examination, order blood
work and other tests, and/or recommend a biopsy. In most cases, a biopsy is the
only way to know for certain whether cancer is present. During a biopsy, the
doctor removes a sample of tissue from the abnormal area. A pathologist studies
the tissue under a microscope to identify cancer cells.

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How is cancer treated?

Cancer treatment can include surgery, radiation therapy, chemotherapy, hormone
therapy, and biological therapy. The doctor may use one method or a combination
of methods, depending on the type and location of the cancer, whether the
disease has spread, the patient's age and general health, and other factors.
Because treatment for cancer can also damage healthy cells and tissues, it
often causes side effects. Some patients may worry that the side effects of
treatment are worse than the disease. However, patients and doctors generally
discuss the treatment options, weighing the likely benefits of killing cancer
cells and the risks of possible side effects. Doctors can suggest ways to
reduce or eliminate problems that may occur during and after treatment.

Surgery is an operation to remove cancer. The side effects of surgery depend on
many factors, including the size and location of the tumor, the type of
operation, and the patient's general health. Patients have some pain after
surgery, but this pain can be controlled with medicine. It is also common for
patients to feel tired or weak for a while after surgery.

Patients may worry that having a biopsy or other type of surgery for cancer
will spread the disease. This is a very rare occurrence because surgeons take
special precautions to prevent cancer from spreading during surgery. Also,
exposing cancer to air during surgery does not cause the disease to spread.

Radiation therapy (also called radiotherapy) uses high-energy rays to kill
cancer cells in a targeted area. Radiation can be given externally by a machine
that aims radiation at the tumor area. It can also be given internally;
needles, seeds, wires, or catheters containing a radioactive substance are
placed directly in or near the tumor. Radiation treatments are painless. The
side effects are usually temporary, and most can be treated or controlled.
Patients are likely to feel very tired, especially in the later weeks of
treatment. Radiation therapy may also cause a decrease in the number of white
blood cells, which help protect the body against infection. With external
radiation, it is also common to have temporary hair loss in the treated area
and for the skin to become red, dry, tender, and itchy.

There is no risk of radiation exposure from coming in contact with a patient
undergoing external radiation therapy. External radiation does not cause the
body to become radioactive. With internal radiation (also called implant
radiation), a patient may need to stay in the hospital, away from other people,
while the radiation level is highest. Implants may be permanent or temporary.
The amount of radiation in a permanent implant goes down to a safe level before
the person leaves the hospital. With a temporary implant, there is no
radioactivity left in the body after the implant is removed.

Chemotherapy is the use of drugs that kill cancer cells throughout the body.
Healthy cells can also be harmed, especially those that divide quickly. The
doctor may use one drug or a combination of drugs. The side effects of
chemotherapy depend mainly on the drug(s) and the dose(s) the patient receives.
Hair loss is a common side effect of chemotherapy; however, not all anticancer
drugs cause loss of hair. Anticancer drugs may also cause temporary fatigue,
poor appetite, nausea and vomiting, diarrhea, and mouth and lip sores. Drugs
that prevent or reduce nausea and vomiting can help with some of these side
effects. Normal cells usually recover when chemotherapy is over, so most side
effects gradually go away after treatment ends.

Hormone therapy is used to treat certain cancers that depend on hormones for
their growth. It works by keeping cancer cells from getting or using the
hormones they need to grow. This treatment may include the use of drugs that
stop the production of certain hormones or that change the way hormones work.
Another type of hormone therapy is surgery to remove organs that make hormones.
For example, the ovaries may be removed to treat breast cancer, or the
testicles may be removed to treat prostate cancer.

Hormone therapy can cause a number of side effects. Patients may feel tired, or
have fluid retention, weight gain, hot flashes, nausea and vomiting, changes in
appetite, and, in some cases, blood clots. Hormone therapy may also cause bone
loss in premenopausal women. Depending on the type of hormone therapy used,
these side effects may be temporary, long lasting, or permanent.

Biological therapy uses the body's immune system, directly or indirectly, to
fight disease and to lessen some of the side effects of cancer treatment.
Monoclonal antibodies, interferon, interleukin-2, and colony-stimulating
factors are some types of biological therapy.

The side effects caused by biological therapy vary with the specific treatment.
In general, these treatments tend to cause flu-like symptoms, such as chills,
fever, muscle aches, weakness, loss of appetite, nausea, vomiting, and
diarrhea. Patients also may bleed or bruise easily, get a skin rash, or have
swelling. These problems can be severe, but they go away after the treatment

Are clinical trials (research studies) available? Where can people get more
information about clinical trials?

Yes. Clinical trials are an important treatment option for many cancer
patients. To develop new, more effective treatments, and better ways to use
current treatments, the NCI is sponsoring clinical trials in many hospitals and
cancer centers around the country. Clinical trials are a critical step in the
development of new methods of treatment. Before any new treatment can be
recommended for general use, doctors conduct clinical trials to find out
whether the treatment is safe for patients and effective against the disease.

People interested in taking part in a clinical trial should talk with their
doctor. Information about clinical trials is available from the NCI's Cancer
Information Service (CIS) (see below) at 1–800–4–CANCER and in the NCI booklet
Taking Part in Cancer Treatment Research Studies, which is available at
http://www.cancer.gov/publications on the Internet. This booklet describes how
research studies are carried out and explains their possible benefits and
risks. Further information about clinical trials is available at
http://www.cancer.gov/clinicaltrials on the NCI's Web site. The Web site offers
detailed information about specific ongoing treatment trials as well as trials
focused on prevention, screening, and diagnosis by linking to PDQ®, the NCI's
comprehensive cancer information database. The CIS also provides information
from PDQ.

Does cancer always cause pain?

Having cancer does not always mean having pain. Whether a patient has pain may
depend on the type of cancer, the extent of the disease, and the patient's
tolerance for pain. Most pain occurs when the cancer grows and presses against
bones, organs, or nerves. Pain may also be a side effect of treatment. However,
pain can generally be relieved or reduced with prescription medicines or
over-the-counter drugs recommended by the doctor. Other ways to reduce pain,
such as relaxation exercises, may also be useful. Pain should not be accepted
as an unavoidable part of having cancer. It is important for patients to talk
about pain so steps can be taken to help relieve it. The fear of addiction or
“losing control” should not stop patients from taking pain medication. Patients
who take medications for cancer pain, as prescribed by their doctor, rarely
become addicted to them. In addition, changing the dose or type of medication
can usually help if the patient has troublesome side effects.
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