Cancer is a collection of diseases in which some cells grow out of control. These cells form solid masses or tumors or invade healthy tissues and organs. Treatment is possible for many cancers.
Cancer is the name for a group of more than 100 related diseases. There are many kinds of cancer, but all cancers start when some of the body's cells grow out of control. Untreated cancers can cause serious illness and death.
Normal body cells grow, divide to make new cells, and die in an orderly way. Cancer starts when cells in a part of the body start to grow and divide uncontrollably. Cancer cell growth is different from normal cell growth. Instead of dying, cancer cells continue to grow and form new, abnormal cells. Cancer cells can also invade (grow into) other tissues, which normal cells cannot do. Growing out of control and invading other tissues are what makes a cell a cancer cell.
Changes to the microscopic, genetic parts of a cell - their deoxyribonucleic acid (DNA) – make cells become cancerous. DNA is in every cell and it directs all its actions. In a normal cell, when DNA is damaged the cell either repairs the damage or dies. In cancer cells, the damaged DNA is not repaired, but the cell still does not die like it should. Instead, the cell goes on making new cells that the body does not need or do not work properly. These new cells all have the same damaged DNA as the first cell does.
People can inherit abnormal or damaged DNA, but most DNA damage is caused by mistakes that happen while a normal cell is reproducing or by something in the environment. Sometimes DNA damage may be caused by exposure to something like cigarette smoking or sun exposure. Still, the exact cause of most cancers is unknown and most cancers are likely caused by a combination of factors.
In most cases, the cancer cells form a tumor or a solid mass. Over time, the tumors can invade nearby normal tissue, crowd it out, or push it aside. Some cancers, like leukemia, rarely form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues where they grow. Cancer cells often travel to other parts of the body where they can grow and form new tumors that crowd out normal tissue. This happens when the cancer cells get into the body’s bloodstream or lymph vessels. The process of cancer spreading is called metastasis.
Different types of cancer can behave very differently. The signs and symptoms of cancer and the treatment options depend on the type of cancer and how long it has been in your body. Most cancer treatments include surgery, radiation, and/or chemotherapy.
Cancer is the second-leading cause of death in the United States. Survival rates are improving for many types of cancer, thanks to improvements in cancer screening and cancer treatment.
Signs and symptoms of cancer vary depending on what part of the body is affected.
Some general signs and symptoms associated with, but not specific to, cancer, include:
- Lump or area of thickening that can be felt under the skin
- Weight changes, including unintended loss or gain
- Skin changes, such as yellowing, darkening or redness of the skin, sores that will not heal, or changes to existing moles
- Changes in bowel or bladder habits
- Persistent cough or trouble breathing
- Difficulty swallowing
- Persistent indigestion or discomfort after eating
- Persistent, unexplained muscle or joint pain
- Persistent, unexplained fevers or night sweats
- Unexplained bleeding or bruising
Cancer is a complex group of diseases with many potential causes, including genetic factors; lifestyle factors such as tobacco use, diet, and physical activity; certain types of infections; and environmental exposures to different types of chemicals and radiation.
Essentially, cancer is a genetic disease: it is caused by changes to genes that control the way our cells function, especially how they grow and divide. Genetic changes that cause cancer can be inherited from our parents. They can also arise as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun.
Each person’s cancer has a unique combination of genetic changes. As the cancer continues to grow, additional changes will occur. Even within the same tumor, different cells may have different genetic changes.
The majority of cancers occur in people who do not have any known risk factors. Factors known to increase your risk of cancer include:
- Your age. Cancer usually takes decades to develop. Most people diagnosed with cancer are 65 or older, but cancer can be diagnosed at any age.
- Your habits. Smoking, drinking more than one alcoholic drink a day (for women of all ages and men older than age 65) or two drinks a day (for men age 65 and younger), excessive exposure to the sun or frequent blistering sunburns, being obese, and having unsafe sex can contribute to cancer.
- Your family history. Only a small portion of cancers are due to an inherited condition. If cancer is common in your family, it is possible that mutations are being passed from one generation to the next. In this case, genetic testing may be able to identify inherited mutations that might increase the risk of certain cancers.
- Your health conditions. Some chronic health conditions, such as ulcerative colitis, can increase your risk of developing certain cancers. Talk to your doctor about your risk.
- Your environment. The environment around you may contain harmful chemicals that can increase your risk of cancer. Even if you do not smoke, you might inhale secondhand smoke if you go where people are smoking or if you live with someone who smokes. Chemicals in your home or workplace, such as asbestos and benzene, also are associated with an increased risk of cancer.
Diagnosing cancer in its earliest stages provides the best chance for a cure. Talk to your doctor about what types of cancer screening may be appropriate for you. For some cancers, screening tests can save lives by diagnosing cancer early. For other cancers, screening tests are recommended only for people with increased risk.
Your doctor may use one or more approaches to diagnose cancer:
- Physical exam. Your doctor may feel areas of your body for lumps that may indicate a tumor. He or she may look for abnormalities, such as changes in skin color or enlargement of an organ, that may indicate the presence of cancer.
- Laboratory tests. Laboratory tests, such as urine and blood tests, may help your doctor identify abnormalities that can be caused by cancer.
- Imaging tests. Imaging tests allow your doctor to examine your bones and internal organs in a noninvasive way. Imaging tests used in diagnosing cancer may include a computerized tomography (CT) scan, bone scan, magnetic resonance imaging (MRI), positron emission tomography (PET) scan, ultrasound and X-ray, among others.
- Biopsy. During a biopsy, your doctor collects a sample of cells for testing in the laboratory. In most cases, a biopsy is the only way to definitively diagnose cancer.
Once cancer is diagnosed, the extent (stage) of your cancer can be determined. The cancer's stage is used to determine the best treatment options and increase chances for a cure. Imaging tests, such as bone scans or X-rays, may be included as part of the staging process to see if cancer has spread to other parts of the body. Cancer stages are generally indicated by Roman numerals — I through IV, with higher numerals indicating more advanced cancer. In some cases, cancer stage is indicated using letters or words.
Living With Cancer
Cancer and its treatment can cause several complications, including:
- Difficulty breathing
- Diarrhea or constipation
- Weight loss
- Chemical changes in your body
- Brain and nervous system problems
- Unusual immune system reactions to cancer
- Cancer that spreads
- Cancer that returns
If you have or have had cancer, you can take steps to manage the stress that accompanies the diagnosis:
- Learn about the type of cancer you have so you can make informed decisions about your care.
- Have a schedule of follow-up tests and go to each appointment.
- Take care of yourself so that you are ready to fight cancer. This includes eating a healthy that includes plenty of fruits, vegetables and whole grains, exercising for at least 30 minutes most days of the week, and getting enough sleep so that you wake feeling rested.
- Accept help and support from family and friends.
- Talk with other cancer survivors or attend support groups.
Many cancer treatments are available. Treatment options will depend on the type and stage of cancer, your general health, and your preferences. Different types of cancer treatments have different goals, including:
- Cure. A cure for cancer will allow you to live a normal life span. This may or may not be possible for all types and stages of cancers.
- Primary treatment. The goal of a primary treatment is to completely remove the cancer from your body or kill the cancer cells. Any cancer treatment can be used as a primary treatment, but the most common primary cancer treatment for the most common cancers is surgery. If your cancer is particularly sensitive to radiation therapy or chemotherapy, you may receive one of those therapies as your primary treatment.
- Adjuvant treatment. The goal of adjuvant therapy is to kill any cancer cells that may remain after primary treatment in order to reduce the chance that the cancer will recur. Any cancer treatment can be used as an adjuvant therapy. Common adjuvant therapies include chemotherapy, radiation therapy, and hormone therapy.
- Palliative treatment. Palliative treatments helps relieve side effects of treatment or signs and symptoms caused by cancer itself. Surgery, radiation, chemotherapy, and hormone therapy can all be used to relieve signs and symptoms. Medications may relieve symptoms such as pain and shortness of breath. Palliative treatment can be used at the same time as other treatments intended to cure your cancer.
Cancer treatment options include:
- Surgery to remove the cancer or as much of the cancer as possible
- Chemotherapy, which uses drugs to kill cancer cells
- Radiation therapy, which uses high-powered energy beams, such as X-rays, to kill cancer cells. Radiation treatment can come from a machine outside your body (external beam radiation), or it can be placed inside your body (brachytherapy).
- Stem cell transplant or bone marrow transplant. Your bone marrow is the material inside your bones that makes blood cells from blood stem cells. A stem cell transplant can use your own stem cells or stem cells from a donor. This type of transplant allows your doctor to use higher doses of chemotherapy to treat your cancer. It may also be used to replace diseased bone marrow.
- Immunotherapy, which is also known as biological therapy, uses your body's immune system to fight cancer. Cancer can survive unchecked in your body because your immune system doesn't recognize it as an intruder. Immunotherapy can help your immune system recognize the cancer and attack it.
- Hormone therapy, which removes or blocks the actions of hormones that fuel the growth of some types of cancer, including breast cancer and prostate cancer.
- Targeted drug therapy, which focuses on specific abnormalities within cancer cells that allow them to survive.