What is cancer?
Cancer is a large group of diseases with one thing in common: They all happen when normal cells become cancerous cells that multiply and spread.
Cancer is the second most common cause of death in the U.S. But fewer people are dying of cancer now than 20 years ago. Early detection and innovative treatments are curing cancer and helping people with cancer live longer. At the same time, medical researchers are identifying independent risk factors linked to developing cancer to help prevent people from developing cancer.
What is the difference between a normal cell and a cancerous cell?
Normally, cells follow instructions provided by genes. Genes set down rules for cells to follow, such as when to start and stop growing. Cancerous cells ignore the rules that normal cells follow:
- Normal cells divide and multiply in a controlled manner. Cancerous cells multiply uncontrollably.
- Normal cells are programmed to die (apoptosis). Cancerous cells ignore those directions.
- Normal cells for solid organs stay put. All cancerous cells are able to move around.
- Normal cells don’t grow as fast as cancerous cells.
How does cancer start in your body?
Cancer starts when a gene or several genes mutate and create cancerous cells. These cells create cancer clusters, or tumors. Cancerous cells may break away from tumors, using your lymphatic system or bloodstream to travel to other areas of your body. (Healthcare providers call this metastasis.)
For example, a tumor in your breast may spread to your lungs, making it hard for you to breathe. In some types of blood cancer, abnormal cells in your bone marrow make abnormal blood cells that multiply uncontrollably. Eventually, the abnormal cells crowd out normal blood cells.
How common is cancer?
According to the American Cancer Society, 1 in 2 men and people assigned male at birth (AMAB) and 1 in 3 women and people assigned female at birth (AFAB) will develop cancer. As of 2019, more than 16.9 million people in the U.S. were living with cancer. The most common cancers in the United States are:
- Breast cancer: Breast cancer is the most common type of cancer. It mostly affects women and people AFAB. But about 1% of all breast cancer cases affect men and people AMAB.
- Lung cancer: Lung cancer is the second most common cancer. There are two types of lung cancer: non-small cell cancer and small cell lung cancer.
- Prostate cancer: This cancer affects 1 in 9 men and people AMAB.
- Colorectal cancer: Colon cancer and rectal cancer affect different parts of your digestive system.
- Blood cancers: Leukemia and lymphoma are the most common blood cancers.
Who’s affected by cancer?
Almost anyone may develop cancer, but data show cancer cases vary based on race and sex. According to the 2022 Annual Report on Cancer, the disease:
- Affects slightly more men and people AMAB than women and people AFAB.
- Affects more Black men (AMAB) than people in other racial groups.
- Affects more women (AFAB) who are American Indian or Alaska natives than people in other racial groups.
Almost anyone may develop cancer, but it typically affects people aged 60 and older.
Symptoms and Causes
What are cancer symptoms?
Cancer is a complicated disease. You can have cancer for years without developing symptoms. Other times, cancer may cause noticeable symptoms that get worse very quickly. Many cancer symptoms resemble other, less serious illnesses. Having certain symptoms doesn’t mean you have cancer. In general, you should talk to a healthcare provider anytime there’s a change in your body that lasts for more than two weeks.
First symptoms of cancer
Some common early cancer symptoms include:
- Unexplained weight loss.
- Chronic tiredness.
- Persistent pain.
- Fever that occurs mostly at night.
- Skin changes, particularly moles that change shape and size or new moles.
Left untreated, cancer may cause additional symptoms, including:
- Bruising or bleeding more easily.
- Lumps or bumps under your skin that don’t go away.
- Difficulty breathing.
- Difficulty swallowing.
What causes cancer?
Cancer is a genetic disorder. It happens when genes that manage cell activity mutate and create abnormal cells that divide and multiply, eventually disrupting how your body works.
Medical researchers estimate 5% to 12% of all cancers are caused by inherited genetic mutations that you can’t control.
More frequently, cancer happens as an acquired genetic mutation. Acquired genetic mutations happen over the course of your life. Medical researchers have identified several risk factors that increase your chance of developing cancer.
Cancer risk factors you can control
- Smoking: Smoking cigarettes and cigars and using e-cigarettes increases your chance of developing lung, pancreatic, esophageal and oral cancer.
- Diet: Eating high-fat or high-sugar foods can increase your risk for many types of cancer. You’re also more vulnerable to disease if you don’t get enough exercise.
- Environment: Exposure to toxins in your environment — such as asbestos, pesticides and radon — can eventually lead to cancer.
- Radiation exposure: Ultraviolet (UV) radiation from the sun significantly increases your risk of developing skin cancer. Over-exposure to radiation treatment can also be a risk factor.
- Hormone therapy: Women and people AFAB taking hormone replacement therapy may have an increased risk for breast cancer and endometrial cancer.
How can I reduce my risk of developing cancer?
You can reduce your risk by changing some of your lifestyle choices:
- If you smoke or use tobacco, try to stop. Ask a healthcare provider about smoking cessation programs that can help you quit tobacco.
- Follow a diet plan that’s healthy for you. If you want help managing your weight, ask a healthcare provider about nutritional guidance and weight management programs.
- Add exercise to your daily routine. Exercise may boost your immune system so it provides more protection against cancer.
- Avoid toxins, including asbestos, radon and pesticides.
- Protect yourself against sun damage.
- Have regular cancer screenings.
Diagnosis and Tests
How do healthcare providers diagnose cancer?
Healthcare providers begin a cancer diagnosis by doing a comprehensive physical examination. They’ll ask you to describe your symptoms. They may ask about your family medical history. They may also do the following tests:
- Blood tests.
- Imaging tests.
Blood tests for cancer may include:
- Complete blood count (CBC): A CBC test measures and counts your blood cells.
- Tumor markers: Tumor markers are substances that cancer cells release or that your normal cells release in response to cancer cells.
- Blood protein tests: Healthcare providers use a process called electrophoresis to measure immunoglobulins. Your immune system reacts to certain cancers by releasing immunoglobulins.
- Circulating tumor cell tests: Cancerous tumors may shed cells. Tracking tumor cells helps healthcare providers monitor cancer activity.
Imaging tests may include:
- Computed tomography (CT) scan: CT scans check for cancerous tumors’ location and impact on your organs and bones.
- X-rays: X-rays use safe amounts of radiation to create images of your bones and soft tissues.
- Positron emission test (PET) scan: PET scans produce images of your organs and tissues at work. Healthcare providers may use this test to detect early signs of cancer.
- Ultrasound: An ultrasound uses high-intensity sound waves that show structures inside of your body.
- Magnetic resonance imaging (MRI): MRIs use a large magnet, radio waves and a computer to create images of your organs and other structures inside of your body.
- Iodine meta-iodobenzylguanidine (MIGB): This nuclear imaging test helps detect cancer, including carcinoid tumors and neuroblastoma.
A biopsy is a procedure healthcare providers do to obtain cells, tissue, fluid or growths that they’ll examine under a microscope. There are several kinds of biopsies:
- Needle biopsy: This test may be called a fine needle aspiration or fine needle biopsy. Healthcare providers use a thin hollow needle and syringe to extract cells, fluid or tissue from suspicious lumps. Needle biopsies are often done to help diagnose breast cancer, thyroid cancer or cancer in your lymph nodes.
- Skin biopsy: Healthcare providers remove a small sample of your skin to diagnose skin cancer.
- Bone marrow biopsy: Healthcare providers remove a small sample of bone marrow so they can test the sample for signs of disease, including cancer in your bone marrow.
- Endoscopic or laparoscopic biopsy: These biopsies use an endoscope or laparoscope to see the inside of your body. With both of these methods, a small cut is made in your skin and an instrument is inserted. An endoscope is a thin, flexible tube with a camera on the tip, along with a cutting tool to remove your sample. A laparoscope is a slightly different scope.
- Excisional or incisional biopsy: For these open biopsies, a surgeon cuts into your body and either the entire tumor is removed (excisional biopsy) or a part of the tumor is removed (incisional biopsy) to test or treat it.
- Perioperative biopsy: This test may be called a frozen section biopsy. This biopsy is done while you’re having another procedure. Your tissue will be removed and tested right away. Results will come in soon after the procedure, so if you need treatment, it can start immediately.
Cancer may happen when a single gene mutates or several genes that work together mutate. Researchers have identified more than 400 genes associated with cancer development. People who inherit these genes from their biological parents may have an increased risk of developing cancer. Healthcare providers may recommend genetic testing for cancer if you have an inherited form of cancer. They may also do genetic testing to do therapy that targets specific cancer genes. They use test results to develop a diagnosis. They’ll assign a number or stage to your diagnosis. The higher the number, the more cancer has spread.
How is cancer stage determined?
Healthcare providers use cancer staging systems to plan treatment and develop a prognosis or expected outcome. TNM is the most widely used cancer staging system. T stands for primary tumor. N stands for lymph nodes and indicates whether a tumor has spread to your lymph nodes. M stands for metastasis, when cancer spreads.
What are the four stages of cancer?
Most cancers have four stages. The specific stage is determined by a few different factors, including the tumor’s size and location:
- Stage I: The cancer is localized to a small area and hasn’t spread to lymph nodes or other tissues.
- Stage II: The cancer has grown, but it hasn’t spread.
- Stage III: The cancer has grown larger and has possibly spread to lymph nodes or other tissues.
- Stage IV: The cancer has spread to other organs or areas of your body. This stage is also referred to as metastatic or advanced cancer.
Though stages one through four are the most common, there’s also a Stage 0. This earliest phase describes cancer that’s still localized to the area in which it started. Cancers that are still in Stage 0 are usually easily treatable and are considered pre-cancerous by most healthcare providers.
Management and Treatment
How do healthcare providers treat cancer?
Healthcare providers may use several different treatments, sometimes combining treatments based on your situation. Common cancer treatments include:
- Chemotherapy: Chemotherapy is one of the most common cancer treatments. It uses powerful drugs to destroy cancer cells. You may receive chemotherapy in pill form or intravenously (through a needle into a vein). In some cases, providers may be able to direct chemotherapy to the specific area affected.
- Radiation therapy: This treatment kills cancer cells with high dosages of radiation. Your healthcare provider may combine radiation therapy and chemotherapy.
- Surgery: Cancerous tumors that haven’t spread may be removed with surgery. Your healthcare provider may recommend therapy. This treatment combines surgery with chemotherapy or radiation to shrink a tumor before surgery or to kill cancer cells that may remain after surgery.
- Hormone therapy: Sometimes, providers prescribe hormones that block other cancer-causing hormones. For example, men and people assigned male at birth who have prostate cancer might receive hormones to keep testosterone (which contributes to prostate cancer) lower than usual.
- Biological response modifier therapy: This treatment stimulates your immune system and helps it perform more effectively. It does this by changing your body’s natural processes.
- Immunotherapy for cancer: Immunotherapy is a cancer treatment that engages your immune system to fight the disease. The treatment may be called biological therapy.
- Targeted therapy for cancer: Targeted therapy is a cancer treatment that targets the genetic changes or mutations that turn healthy cells into cancer cells.
- Bone marrow transplant: Also called stem cell transplantation, this treatment replaces damaged stem cells with healthy ones. Autologous transplantation uses your supply of healthy stem cells. Allogeneic transplantation uses stem cells donated by another person.
What are cancer treatment side effects?
Healthcare providers work to balance the treatment so it destroys cancer without harmful or lasting side effects. Even so, all cancer treatments have side effects. Some treatments cause side effects that last for years after treatment is completed. Many people benefit from palliative care that eases cancer symptoms and treatment side effects. The most common cancer treatment side effects are:
Outlook / Prognosis
What is the prognosis/outlook for cancer?
Right now, more people are being cured of cancer or living longer with cancer. In general, people with cancer that were diagnosed and treated before it could spread have a good outlook.
But you’re unique, and so is your cancer prognosis. Your healthcare providers will base your prognosis on factors such as:
- Your overall health.
- The type of cancer you have.
- The stage of your cancer.
- How you may respond to treatment.
- Your overall health, the type of cancer that you have, its stage and how you respond to treatment all affect your prognosis.
Your healthcare provider is your best resource for prognosis information. They know your situation and they know you.
What are cancer survival rates?
Survival rates are estimates based on the experiences of large groups of people who have different kinds of cancer. Like prognoses, cancer survival rates vary based on cancer type, stage and treatment. According to the most recent data from the National Cancer Institute, 68% of people with any kind of cancer were alive five years after their diagnosis.
How do I live with cancer?
Self-care is an important part of living with cancer. Some self-care suggestions include:
- Establish good eating and exercise habits. Ask to speak with a nutritionist for healthy menu ideas.
- Fatigue is a common symptom and treatment side effect. Pay attention to your body and rest when you need to, not just when you can.
- You may be living with cancer for a long time. That’s good news, of course, but chronic illness may be challenging. Talking to a mental health professional or finding a support group may help you navigate challenges.
What is cancer survivorship?
If you have cancer, you are a cancer survivor. Cancer survivorship starts the day you receive a cancer diagnosis and continues for the rest of your life. As a cancer survivor, you’re likely to experience many challenges or complications.
Cancer that comes back
Sometimes, cancer treatment doesn’t eliminate all cancerous cells. Those cells can become new cancerous tumors. Cancer that comes back, or recurrent cancer, may appear at the same place as the original cancer, in nearby lymph nodes or spread to organs and tissues far away from the original site.
A second cancer is a new cancer. People who have second cancers may have cancer in the same organ or area of their body as the first cancer, but it’s a different type of cancer from what it was before. They may also have cancer in different areas of their bodies. Second cancers are more common, as more people live longer with cancer.
Cancer fatigue is an overwhelming sense of tiredness that isn’t helped by getting more rest. Some people have chronic cancer fatigue that continues after they’ve finished treatment.
Some cancer treatments have lasting side effects that may cause pain. One study found that 39% of people who completed cancer treatment had chronic pain. Peripheral neuropathy is an example of pain that may persist after treatment.
Chemotherapy brain fog
Chemotherapy brain fog (chemo brain) happens when cancer or cancer treatment affects your ability to remember or act on information. About 75% of people receiving cancer treatment tell their healthcare providers that they have issues with memory, concentration and their ability to complete tasks.
When should I see my healthcare provider?
Talk to your healthcare provider about any issues you experience while you’re undergoing cancer treatment. Call your oncology team if you notice:
- A fever of 101 degrees Fahrenheit (38.33 degrees Celsius) or higher.
- Severe headaches.
- Persistent cough.
- Shortness of breath (dyspnea).
- Sores on your lips or in your mouth.
- Sudden weight loss greater than five pounds.
- Excessive vomiting (three times an hour for three hours or more).
- Blood in your urine (pee) or feces (poop).
- Excessive bleeding or bruising.
What questions should I ask my healthcare provider?
Knowledge is power. If you’ve been diagnosed with cancer, you’ll want to gather as much information as you can. Here are some questions to ask your healthcare provider:
- What type of cancer do I have?
- Has the cancer spread to other areas of my body?
- Is my cancer genetic?
- What are my chances of survival?
- Which treatments do you recommend?
- What are the risks and benefits of my treatment?
- How long will treatment take?
- Will I be able to work during cancer treatment?
- Will cancer treatment affect my fertility?
- Will I need to stay in the hospital for my treatment?
- Would a clinical trial be a good option for me?
A note from Cleveland Clinic
The words “you have cancer” may be one of the hardest things anyone has to hear. Learning you have cancer might make you feel frightened and overwhelmed. Many people feel as if they’ve lost control of their lives. Your healthcare providers understand all of those feelings. They know a cancer diagnosis is a life-changing event. They also know cancer treatment is a stressful journey. If you have cancer, know your providers will be with you every step of the way.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy