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

What is cancer?

Cancer is one of the scariest words in the English language. When you hear the word as part of a diagnosis, it's natural to feel many emotions, especially fear.

A cancer diagnosis can cause you and your family a great deal of stress, but you have many resources to help you. You owe it to yourself to learn as much as possible about your diagnosis and how it can be treated. Knowledge is power, and it can help you deal with this disease.

Cancer is a disease that occurs when cells in the body begin to divide at a faster rate than the body requires. These rapidly dividing cells grow into a lump that is known as a tumor. The tumor can be benign (non-cancerous) or malignant (cancerous).

What is cancer staging?

One of the biggest concerns about a cancer diagnosis is whether the cancer has spread (metastasized) beyond its original location. To determine this, the doctor assigns a number (I through IV) to your diagnosis. The higher the number, the more the cancer has spread throughout your body. This is called "staging." The doctor needs this information in order to plan your treatment.

What are the causes of cancer?

Many factors can cause the development of cancer in the body. Some of these factors, such as heredity (family members who have the disease) cannot be avoided. Others, such as lifestyle, can be controlled.

For instance, the use of tobacco is one of the main causes of cancer, especially lung cancer. Tobacco use, whether in the form of smoking, chewing, or exposure to second-hand smoke (smoking by others), can also cause cancer of the mouth and larynx, esophagus, throat, and many other parts of the body.

Other primary causes of cancer include:

  • Diet/nutrition: The proper diet is always important, but a poor diet might also increase your risk of cancer. For instance, eating large amounts of high-fat foods can contribute to cancer of the colon and prostate. Exercise is also key. Excess weight might be a contributing factor for various types of cancer, including breast, uterus, ovary, prostate, and colon.
  • Environment: Cancer can develop if the person is exposed over a period of time to various chemicals in the environment, including pesticides, asbestos, and radon.
  • Exposure to radiation: Too much exposure to the sun (ultraviolet radiation) can cause skin cancer. In addition, over-exposure to X-rays or to radiation therapy (as part of cancer treatment) might be a risk factor for cancer.
  • Hormone therapy: Women who are going through menopause might receive a prescription for hormone replacement therapy, either estrogen alone or in combination with progesterone. The use of both of these hormones together has been shown to increase the risk of breast cancer. A woman who still has her uterus and is taking estrogen alone (without progesterone) has a greater risk of endometrial cancer.

What are the symptoms of cancer?

The most prominent symptoms of cancer include the following:

  • A sore that doesn't heal
  • A wart or mole that changes
  • An unusual lump anywhere in the body
  • A persistent cough/hoarseness
  • Indigestion or problems swallowing
  • Changes in bowel movement or urination habits
  • Unusual weight loss
  • Unusual bleeding or discharge from various parts of the body

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