Cancer is the uncontrolled growth of abnormal cells in the body. Cancerous cells are also called malignant cells.


Cancer grows out of cells in the body. Normal cells multiply when the body needs them, and die when they are damaged or the body doesn't need them.

Cancer appears to occur when the genetic material of a cell becomes changed. This results in cells growing out of control. Cells divide too quickly and do not die in a normal way.

There are many kinds of cancer. Cancer can develop in almost any organ or tissue, such as the lung, colon, breast, skin, bones, or nerve tissue.

There are many risk factors for cancer, including:

The cause of many cancers remains unknown.

The most common cause of cancer-related death is lung cancer.

In the U.S., skin cancer is the most commonly diagnosed cancer.

In U.S. men, other than skin cancer the three most common cancers are:

In U.S. women, other than skin cancer the three most common cancers are:

Some cancers are more common in certain parts of the world. For example, in Japan, there are many cases of stomach cancer. But in the United States, this type of cancer is less common. Differences in diet or environmental factors may play a role.

Some other types of cancer include:


Symptoms of cancer depend on the type and location of the cancer. For example, lung cancer can cause coughing, shortness of breath, or chest pain. Colon cancer often causes diarrhea, constipation, and blood in the stool.

Some cancers may not have any symptoms. In certain cancers, such as pancreatic cancer, symptoms often do not start until the disease has reached an advanced stage.

The following symptoms may occur with cancer:

Exams and Tests

Like symptoms, the signs of cancer vary based on the type and location of the tumor. Common tests include the following:

Most cancers are diagnosed by biopsy. Depending on the location of the tumor, the biopsy may be a simple procedure or a serious operation. Most patients with cancer have CT scans to determine the exact location and size of the tumor or tumors.

A cancer diagnosis is often difficult to cope with. It is important that you discuss the type, size, and location of the cancer with your health care provider when you are diagnosed. You also will want to ask about treatment options, along with their benefits and risks.

It's a good idea to have someone with you at the provider's office to help you get through the diagnosis. If you have trouble asking questions after hearing about your diagnosis, the person you bring with you can ask them for you.


Treatment varies based on the type of cancer and its stage. The stage of a cancer refers to how much it has grown and whether the tumor has spread from its original location.

Although treatment for cancer can be difficult, there are many ways to keep up your strength.

If you have radiation treatment:

If you have chemotherapy:

Talk with family, friends, or a support group about your feelings. Work with your health care providers throughout your treatment. Helping yourself can make you feel more in control.

Support Groups

The diagnosis and treatment of cancer often causes a lot of anxiety and can affect a person's entire life. There are many resources for cancer patients.

Outlook (Prognosis)

The outlook depends on the type of cancer and the stage of the cancer when diagnosed.  

Some cancers can be cured. Other cancers that are not curable can still be treated effectively. Some patients can live for many years with cancer. Other tumors are quickly life threatening.

Possible Complications

Complications depend on the type and stage of cancer. The cancer may spread.

When to Contact a Medical Professional

Contact your health care provider if you develop symptoms of cancer.


You can reduce the risk of getting a cancerous (malignant) tumor by:

Cancer screenings, such as mammography and breast examination for breast cancer and colonoscopy for colon cancer, may help catch these cancers at their early stages when they are most treatable. Some people at high risk for developing certain cancers can take medication to reduce their risk.

Review Date: 1/18/2015
Reviewed By: Laura J. Martin, MD, MPH, ABIM Board Certified in Internal Medicine and Hospice and Palliative Medicine, Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

This information should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. © 1997- 2007 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.