What is cancer?

Cancer is a disease that develops when cells in your body divide at a faster rate than normal. These abnormal cells grow into a lump — or tumor.

How is the stage of cancer determined?

Your healthcare provider will perform tests to determine the extent and severity of your cancer. A number will then be assigned to your diagnosis. The higher the number, the more cancer has spread.

What are the four stages of cancer?

Most cancers have four stages. The specific stage is determined by a few different factors, including the size and location of the tumor:

  • Stage I: Cancer is localized to a small area and hasn’t spread to lymph nodes or other tissues.
  • Stage II: Cancer has grown, but it hasn’t spread.
  • Stage III: Cancer has grown larger and has possibly spread to lymph nodes or other tissues.
  • Stage IV: Cancer has spread to other organs or areas of your body. This stage is also referred to as metastatic or advanced cancer.

Though stages I through IV are the most common, there is also stage zero. This earliest phase describes cancer that is still localized to the area in which it started. Cancers that are still in stage zero are usually easily treatable and are considered pre-cancerous by most healthcare providers.

What are the 5 types of cancer?

There are five main types of cancer. These include:

  • Carcinoma. This type of cancer affects organs and glands, such as the lungs, breasts, pancreas and skin. Carcinoma is the most common type of cancer.
  • Sarcoma. This cancer affects soft or connective tissues, such as muscle, fat, bone, cartilage or blood vessels.
  • Melanoma. Sometimes cancer can develop in the cells that pigment your skin. These cancers are called melanoma.
  • Lymphoma. This cancer affects your lymphocytes or white blood cells.
  • Leukemia. This type of cancer affects blood.

How common is cancer?

Cancer is a common disease that can affect almost every part of your body. About 39.5% of all people will be diagnosed with cancer at some point in their lives.

How does cancer start in your body?

Cancer occurs when your genes stop controlling the way your cells divide. For example, instead of old cells dying, they grow and form abnormal cells.

How dangerous is cancer?

Cancer is potentially fatal. Currently, it’s the leading cause of death worldwide. However, fatality rates largely depend on the type of cancer and how far it has spread. Many types of cancer are successfully treated with prompt care.

Why is cancer so deadly?

When cancer cells develop, they can disturb proper organ function. This can result in reduced oxygen supply and a buildup of waste products. If vital organ function is impaired, it can lead to death.

Symptoms and Causes

What causes cancer?

Several factors contribute to the development of cancer in your body. Smoking and using tobacco products is one of the main causes of:

Other causes of cancer include:

  • An unhealthy lifestyle. 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.
  • A toxic environment. Exposure to toxins in your environment, such as asbestos, pesticides and radon, can eventually lead to cancer.
  • Radiation exposure. Ultraviolet radiation from the sun significantly increases your risk for skin cancer. Over-exposure to radiation treatment can also be a risk factor.
  • Hormone therapy. Women who are taking hormone replacement therapy may have an increased risk for breast cancer and endometrial cancer.

What is the first sign of cancer?

Cancer symptoms can vary significantly for each person. However, there are a few things that could indicate the early signs of disease. Schedule an appointment with your healthcare provider if you experience:

  • Unexplained weight loss.
  • Chronic tiredness.
  • Persistent pain.
  • Fever that occurs mostly at night.
  • Skin changes.

What are common signs of cancer?

As time goes on, you may notice other cancer symptoms surfacing. These may include:

Please note that these symptoms do not mean that you definitely have cancer. However, if any of these symptoms appear, you should see your healthcare provider right away.

How does cancer spread?

When cancer spreads, the cancer cells break away from the original tumor, travel through the body via your bloodstream or lymphatic system, then form new tumors in other areas. This process is called metastasis.

Diagnosis and Tests

How is cancer diagnosed?

In order to treat your cancer, your healthcare provider needs to know the location of the tumor, the stage (whether it has spread) and whether you are strong enough to handle the treatment. They will perform a comprehensive examination and ask you about your symptoms. They may also order certain tests, including:

Management and Treatment

How is cancer treated?

Once your medical team has given you a diagnosis, they’ll design a personalized treatment plan based on their findings. Cancer treatment may include:

  • Chemotherapy. One of the most common cancer treatments, chemotherapy uses powerful drugs to destroy cancer cells. Chemotherapy may be given through an IV or in pill form.
  • Radiation therapy. This treatment kills cancer cells with high dosages of radiation. In some instances, radiation may be given at the same time as chemotherapy.
  • Surgery. In some cases, your surgeon can surgically remove the tumor.
  • Hormone therapy. Sometimes hormones can block other cancer-causing hormones. For example, men with prostate cancer might be given hormones to keep testosterone (which contributes to prostate cancer) at bay.
  • 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. Sometimes called biological therapy, immunotherapy treats disease by using the power of your body’s immune system. It can target cancer cells while leaving healthy cells intact.
  • Bone marrow transplant. Also called stem cell transplantation, this treatment replaces damaged stem cells with healthy ones. Prior to transplantation, you’ll undergo chemotherapy to prepare your body for the process.

What are the side effects of cancer treatment?

People who undergo cancer treatment may experience a wide range of side effects. The exact side effects that you experience will depend on the type of cancer treatment you receive. Listed below are common side effects for various types of cancer treatment:



  • Fatigue.
  • Hair loss.
  • Skin problems.


Hormone therapy

Biological response modifier therapy/immunotherapy

  • Fever.
  • Chills.
  • Muscle aches.
  • Skin rash.
  • Swelling.
  • Increased bruising or bleeding.

Stem cell transplantation

  • Nausea.
  • Vomiting.
  • Flu-like symptoms.
  • Greater risk of infection.

How can I manage side effects of cancer treatment?

If you’re undergoing cancer treatment, talking with your healthcare provider can help you manage your side effects. Many people find that maintaining a healthy diet helps them feel better and stay stronger. You may also benefit from incorporating exercise into your daily routine. Be sure to clear any dietary changes and activities with your healthcare provider first.

How long does it take to recover from cancer treatment?

Because cancer treatments vary significantly, the answer to this question is different for each person. Ask your healthcare provider what to expect in terms of your recovery timeline.


How can I reduce my risk for cancer?

Though cancer can’t be prevented altogether, there are certain things you can do to reduce your risk. For example:

  • Don’t smoke or use other tobacco products.
  • Stay physically active.
  • Eat a healthy diet.
  • Practice safe sex.
  • Use proper daily sun protection.
  • Get vaccinated.

Outlook / Prognosis

What can I expect if I have cancer?

Hearing that you have cancer can be scary, saddening and even frustrating. It’s important to be frank with your healthcare provider about how you’re feeling. Finding a support group can also help you cope while you’re on your journey. Cancer treatment options vary, so talk to your healthcare provider about what to expect.

Living With

When should I see my healthcare provider?

If you’re undergoing cancer treatment, it’s important to bring any issues to the attention of your healthcare provider. Call your oncology team if you notice:

  • A fever of 101° or higher.
  • Severe headaches.
  • Chills.
  • Persistent cough.
  • Shortness of breath (dyspnea).
  • Sores on your lips or in your mouth.
  • Sudden weight loss of over five pounds.
  • Excessive vomiting (three times an hour for three hours or more).
  • Blood in your pee or 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?
  • What are my chances of survival?
  • What 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 be hospitalized?
  • Would a clinical trial be a good option for me?

A note from Cleveland Clinic

If you’ve been diagnosed with cancer, you may understandably feel sad, fearful or even angry. The good news is that there are plenty of resources available to help you cope, including support groups for nearly every type of cancer.

In addition, your healthcare provider can refer you to a counselor who can help you deal with the emotional aspects of your diagnosis. A social worker can also help you with the practical and financial issues related to the disease.

Undergoing cancer treatment can be a stressful journey. But your healthcare team can give you the resources you need to focus on healing and preserve your quality of life.

Last reviewed by a Cleveland Clinic medical professional on 09/08/2021.


  • American Cancer Society. Learn About Cancer ( Accessed 9/17/2021.
  • American Society of Clinical Oncology. Stages of Cancer. Accessed 9/17/2021.
  • MedlinePlus. Cancer: Living with Cancer ( Accessed 9/17/2021.
  • National Cancer Institute. About Cancer ( Accessed 9/17/2021.
  • National Cancer Institute. Cancer Statistics. ( Accessed 9/17/2021.
  • National Cancer Institute. What is Cancer? ( Accessed 9/17/2021.

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