Cancer begins in cells, the building blocks that form tissues. Tissues make up the organs of the body.
Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, they die, and new cells take their place.
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. These extra cells can form a mass of tissue called a growth or tumor.
Tumors can be benign or malignant:
- Benign tumors are not cancer:
- Benign tumors are rarely life-threatening.
- Generally, benign tumors can be removed, and they usually do not grow back.
- Cells from benign tumors do not invade the tissues around them.
- Cells from benign tumors do not spread to other parts of the body.
- Malignant tumors are cancer:
- Malignant tumors are generally more serious than benign tumors. They may be life-threatening.
- Malignant tumors often can be removed, but sometimes they grow back.
- Cells from malignant tumors can invade and damage nearby tissues and organs.
- Cells from malignant tumors can spread (metastasize) to other parts of the body. Cancer cells spread by breaking away from the original (primary) tumor and entering the bloodstream or lymphatic system. The cells can invade other organs, forming new tumors that damage these organs. The spread of cancer is called metastasis.
Most cancers are named for where they start. For example, lung cancer starts in the lung, and breast cancer starts in the breast. Lymphoma is cancer that starts in the lymphatic system. And leukemia is cancer that starts in white blood cells (leukocytes).
When cancer spreads and forms a new tumor in another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if prostate cancer spreads to the bones, the cancer cells in the bones are actually prostate cancer cells. The disease is metastatic prostate cancer, not bone cancer. For that reason, it is treated as prostate cancer, not bone cancer. Doctors sometimes call the new tumor "distant" or metastatic disease.
Doctors often cannot explain why one person develops cancer and another does not. But research shows that certain risk factors increase the chance that a person will develop cancer.
Over time, several factors may act together to cause normal cells to become cancerous. When thinking about your risk of getting cancer, these are some things to keep in mind:
- Not everything causes cancer.
- Cancer is not caused by an injury, such as a bump or bruise.
- Cancer is not contagious. Although being infected with certain viruses or bacteria may increase the risk of some types of cancer, no one can "catch" cancer from another person.
- Having one or more risk factors does not mean that you will get cancer. Most people who have risk factors never develop cancer.
- Some people are more sensitive than others to the known risk factors.
These are the most common risk factors for cancer:
Most cancers occur in people over the age of 65. But people of all ages, including children, can get cancer, too.
Tobacco use is the most preventable cause of death. Using tobacco products or regularly being around tobacco smoke (environmental or secondhand smoke) increases the risk of cancer.
Smokers are more likely than nonsmokers to develop cancer of the lung, larynx (voice box), mouth, esophagus, bladder, kidney, throat, stomach, pancreas, or cervix. They also are more likely to develop acute myeloid leukemia (cancer that starts in blood cells).
People who use smokeless tobacco (snuff or chewing tobacco) are at increased risk of cancer of the mouth.
Ultraviolet (UV) radiation comes from the sun, sunlamps, and tanning booths. It causes early aging of the skin and skin damage that can lead to skin cancer.
This kind of radiation comes from rays that enter the Earth's atmosphere from outer space, radioactive fallout, radon gas, x-rays, and other sources.
Medical procedures are a common source of radiation:
- Doctors use radiation (low-dose x-rays) to take pictures of the inside of the body. These pictures help to diagnose broken bones and other problems.
- Doctors use radiation therapy (high-dose radiation from large machines or from radioactive substances) to treat cancer.
Certain Chemicals and Other Substances
People who have certain jobs (such as painters, construction workers, and those in the chemical industry) have an increased risk of cancer. Many studies have shown that exposure to asbestos, benzene, benzidine, cadmium, nickel, or vinyl chloride in the workplace can cause cancer.
Some Viruses and Bacteria
Being infected with certain viruses or bacteria may increase the risk of developing cancer:
- Human papillomaviruses (HPVs): HPV infection is the main cause of cervical cancer.
- Hepatitis B and hepatitis C viruses: Liver cancer can develop after many years of infection with hepatitis B or hepatitis C.
- Human T-cell leukemia/lymphoma virus (HTLV-1): Infection with HTLV-1 increases a person's risk of lymphoma and leukemia.
- Human immunodeficiency virus (HIV): HIV is the virus that causes AIDS. People who have HIV infection are at greater risk of cancer, such as lymphoma and a rare cancer called Kaposi's sarcoma.
- Epstein-Barr virus (EBV): Infection with EBV has been linked to an increased risk of lymphoma.
- Human herpesvirus 8 (HHV8): This virus is a risk factor for Kaposi's sarcoma.
- Helicobacter pylori : This bacterium can cause stomach ulcers. It also can cause stomach cancer and lymphoma in the stomach lining.
Doctors may recommend hormones (estrogen alone or estrogen along with progestin) to help control problems (such as hot flashes, vaginal dryness, and thinning bones) that may occur during menopause.
Family History of Cancer
Most cancers develop because of changes (mutations) in genes. A normal cell may become a cancer cell after a series of gene changes occur. Some gene changes that increase the risk of cancer are passed from parent to child. These changes are present at birth in all cells of the body.
Having more than two drinks each day for many years may increase the chance of developing cancers of the mouth, throat, esophagus, larynx, liver, and breast. The risk increases with the amount of alcohol that a person drinks. For most of these cancers, the risk is higher for a drinker who uses tobacco.
Poor Diet, Lack of Physical Activity, or Being Overweight
People who have a poor diet, do not have enough physical activity, or are overweight may be at increased risk of several types of cancer. Lack of physical activity and being overweight are risk factors for cancers of the breast, colon, esophagus, kidney, and uterus. Choose a diet rich in fruits and vegetables.
Some types of cancer can be found before they cause symptoms. Checking for cancer (or for conditions that may lead to cancer) in people who have no symptoms is called screening.
Screening can help doctors find and treat some types of cancer early. Generally, cancer treatment is more effective when the disease is found early.
Screening tests are used widely to check for cancers of the breast, cervix, colon, and rectum:
- Breast: A mammogram is the best tool doctors have to find breast cancer early. A mammogram is a picture of the breast made with x-rays.
- Cervix: The Pap test (sometimes called Pap smear) is used to check cells from the cervix. Women should begin having Pap tests 3 years after they begin having sexual intercourse, or when they reach age 21 (whichever comes first). Most women should have a Pap test at least once every 3 years.
- Colon and rectum: A number of screening tests are used to detect polyps (growths), cancer, or other problems in the colon and rectum. People aged 50 and older should be screened.
- Fecal occult blood test: This test can detect tiny amounts of blood in the stool.
- Double-contrast barium enema
- Digital rectal exam
They weigh factors related to the test and to the cancer that the test can detect. For example, doctors think about the person's age, medical history, general health, family history, and lifestyle.
Cancer can cause many different symptoms. These are some of them:
- A thickening or lump in the breast or any other part of the body
- A new mole or a change in an existing mole
- A sore that does not heal
- Hoarseness or a cough that does not go away
- Changes in bowel or bladder habits
- Discomfort after eating
- A hard time swallowing
- Weight gain or loss with no known reason
- Unusual bleeding or discharge
- Feeling weak or very tired
Most often, these symptoms are not due to cancer. They may also be caused by benign tumors or other problems. Usually, early cancer does not cause pain. If you have symptoms, do not wait to feel pain before seeing a doctor.
If you have a symptom or your screening test result suggests cancer, the doctor must find out whether it is due to cancer or to some other cause.
Tests of the blood, urine, or other fluids can help doctors make a diagnosis. These tests can show how well an organ (such as the kidney) is doing its job. Also, high amounts of some substances may be a sign of cancer.
Imaging procedure create pictures of areas inside your body that help the doctor see whether a tumor is present. These pictures can be made in several ways:
- CT scan
- Radionuclide scan
- PET scan
In most cases, doctors need to do a biopsy to make a diagnosis of cancer. For a biopsy, the doctor removes a sample of tissue and sends it to a lab. A pathologist looks at the tissue under a microscope for diagnosis of cancer.
To plan the best treatment for cancer, the doctor needs to know the extent (stage) of your disease. For most cancers (such as breast, lung, prostate, or colon cancer), the stage is based on the size of the tumor and whether the cancer has spread to lymph nodes or other parts of the body.
Your doctor may refer you to a specialist, or you may ask for a referral. Specialists who treat cancer include surgeons, medical oncologists, hematologists, and radiation oncologists.
Getting a Second Opinion
Before starting treatment, you may want a second opinion about your diagnosis and treatment plan. Many insurance companies will cover a second opinion if your doctor requests it. It may take some time and effort to gather medical records and arrange to see another doctor. Usually it is not a problem to take several weeks to get a second opinion. In most cases, the delay in starting treatment will not make treatment less effective.
The treatment plan depends mainly on the type of cancer and the stage of the disease.
Doctors also consider the patient's age and general health. Most treatment plans include surgery, radiation therapy, or chemotherapy. Some involve hormone therapy or biological therapy. In addition, stem cell transplantation may be used so that a patient can receive very high doses of chemotherapy or radiation therapy.
Some cancers respond best to a single type of treatment. Others may respond best to a combination of treatments.
Treatments may work in a specific area (local therapy) or throughout the body (systemic therapy):
- Local therapy removes or destroys cancer in just one part of the body. Surgery to remove a tumor is local therapy. Radiation to shrink or destroy a tumor also is usually local therapy.
- Systemic therapy sends drugs or substances through the bloodstream to destroy cancer cells all over the body. It kills or slows the growth of cancer cells that may have spread beyond the original tumor. Chemotherapy, hormone therapy, and biological therapy are usually systemic therapy.
Your doctor can describe your treatment choices and the expected results. You and your doctor can work together to decide on a treatment plan that is best for you.
Because cancer treatments often damage healthy cells and tissues, side effects are common. Side effects depend mainly on the type and extent of the treatment. Side effects may not be the same for each person, and they may change from one treatment session to the next.
In most cases, the surgeon removes the tumor and some tissue around it. Removing nearby tissue may help prevent the tumor from growing back. The surgeon may also remove some nearby lymph nodes.
It takes time to heal after surgery. The time needed to recover is different for each type of surgery. It is also different for each person. It is common to feel tired or weak for a while.
Some people worry that having surgery (or even a biopsy) for cancer will spread the disease. This seldom happens. Surgeons use special methods and take many steps to prevent cancer cells from spreading. For example, if they must remove tissue from more than one area, they use different tools for each one. This approach helps reduce the chance that cancer cells will spread to healthy tissue.
Similarly, some people worry that exposing cancer to air during surgery will cause the disease to spread. This is not true. Air does not make cancer spread.
Radiation therapy (also called radiotherapy) uses high-energy rays to kill cancer cells. Doctors use several types of radiation therapy. Some people receive a combination of treatments:
- External radiation: The radiation comes from a large machine outside the body. Most people go to a hospital or clinic for treatment 5 days a week for several weeks.
- Internal radiation (implant radiation or brachytherapy): The radiation comes from radioactive material placed in seeds, needles, or thin plastic tubes that are put in or near the tissue,
- Systemic radiation: The radiation comes from liquid or capsules containing radioactive material that travels throughout the body. The patient swallows the liquid or capsules or receives an injection.
The side effects of radiation therapy depend mainly on the dose and type of radiation you receive and the part of your body that is treated. For example, radiation to your abdomen can cause nausea, vomiting, and diarrhea. Your skin in the treated area may become red, dry, and tender. You also may lose your hair in the treated area.
Fortunately, most side effects go away in time
Chemotherapy is the use of drugs that kill cancer cells. Most patients receive chemotherapy by mouth or through a vein. Either way, the drugs enter the bloodstream and can affect cancer cells all over the body.
Chemotherapy is usually given in cycles. People receive treatment for one or more days. Then they have a recovery period of several days or weeks before the next treatment session.
Side effects depend mainly on the specific drugs and the dose. The drugs affect cancer cells and other cells that divide rapidly:
- Blood cells: When drugs damage healthy blood cells, you are more likely to get infections, to bruise or bleed easily, and to feel very weak and tired.
- Cells in hair roots: Chemotherapy can cause hair loss. Your hair will grow back, but it may be somewhat different in color and texture.
- Cells that line the digestive tract: Chemotherapy can cause poor appetite, nausea and vomiting, diarrhea, or mouth and lip sores.
Some drugs can affect fertility. Women may be unable to become pregnant, and men may not be able to father a child.
Although the side effects of chemotherapy can be distressing, most of them are temporary. Your doctor can usually treat or control them.
Some cancers need hormones to grow. Hormone therapy keeps cancer cells from getting or using the hormones they need. It is systemic therapy.
Hormone therapy uses drugs or surgery:
- Drugs: The doctor gives medicine that stops the production of certain hormones or prevents the hormones from working.
- Surgery: The surgeon removes organs (such as the ovaries or testicles) that make hormones.
The side effects of hormone therapy depend on the type of therapy. They include weight gain, hot flashes, nausea, and changes in fertility. In women, hormone therapy may make menstrual periods stop or become irregular and may cause vaginal dryness. In men, hormone therapy may cause impotence, loss of sexual desire, and breast growth or tenderness.
Biological therapy is another type of systemic therapy. It helps the immune system (the body's natural defense system) fight cancer.
Most other types of biological therapy are given through a vein. The biological therapy travels through the bloodstream. Some people get a rash where the therapy is injected. Some have flu-like symptoms such as fever, chills, headache, muscle aches, fatigue, weakness, and nausea. Biological therapy also can cause more serious side effects, such as changes in blood pressure and breathing problems
Stem Cell Transplantation
Transplantation of blood-forming stem cells enables patients to receive high doses of chemotherapy, radiation, or both. The high doses destroy both cancer cells and normal blood cells in the bone marrow. After the treatment, the patient receives healthy, blood-forming stem cells through a flexible tube placed in a large vein. New blood cells develop from the transplanted stem cells. Stem cells may be taken from the patient before the high-dose treatment, or they may come from another person.
The side effects of high-dose therapy and stem cell transplantation include infection and bleeding. In addition, graft-versus-host disease (GVHD) may occur in people who receive stem cells from a donor. In GVHD, the donated stem cells attack the patient's tissues. Most often, GVHD affects the liver, skin, or digestive tract. GVHD can be severe or even fatal. It can occur any time after the transplant, even years later. Drugs may help prevent, treat, or control GVHD.
Nutrition and Physical Activity
It is important for people with cancer to take care of themselves. Taking care of yourself includes eating well and staying as active as you can.
You need enough calories to maintain a good weight. You also need enough protein to keep up your strength. Eating well may help you feel better and have more energy.
Sometimes, especially during or soon after treatment, you may not feel like eating. You may be uncomfortable or tired. You may find that foods do not taste as good as they used to.
Many people find they feel better when they stay active. Walking, yoga, swimming, and other activities can keep you strong and increase your energy. Exercise may reduce nausea and pain and make treatment easier to handle. It also can help relieve stress.