A tumor is an abnormal growth of body tissue. Tumors can be cancerous (malignant) or noncancerous (benign).
In general, tumors occur when cells divide and grow excessively in the body. Normally, the body controls cell growth and division. New cells are created to replace older ones or to perform new functions. Cells that are damaged or no longer needed die to make room for healthy replacements.
If the balance of cell growth and death is disturbed, a tumor may form.
Problems with the body's immune system can lead to tumors. Tobacco causes more deaths from cancer than any other environmental substance. Other risk factors for cancer include:
Benzene and other chemicals and toxins
Drinking too much alcohol
Environmental toxins, such as certain poisonous mushrooms and a type of poison that can grow on peanut plants (aflatoxins)
Excessive sunlight exposure
Types of tumors known to be caused by viruses are:
Some tumors are more common in one gender than the other. Some are more common among children or the elderly. Others are related to diet, environment, and family history.
Symptoms depend on the type and location of the tumor. For example, lung tumors may cause coughing, shortness of breath, or chest pain. Tumors of the colon can cause weight loss, diarrhea, constipation, iron deficiency anemia, and blood in the stool.
Some tumors may not cause any symptoms. Others, such as pancreatic cancer, do not usually cause symptoms until the disease has reached an advanced stage.
Your doctor or nurse might see a tumor, such as skin cancer. But most cancers cannot be seen during an exam because they are deep inside the body.
When a tumor is found, a piece of the tissue is removed and examined under a microscope. This is called a biopsy. It is done to determine if the tumor is noncancerous (benign) or cancerous (malignant). Depending on the location of the tumor, the biopsy may be a simple procedure or a serious operation.
A CT or MRI scan can determine the exact location of the tumor and how far it has spread. Another imaging test called positron emission tomography (PET) is used to find certain tumor types.
The outlook varies greatly for different types of tumors. If the tumor is benign, the outlook is generally very good. But a benign tumor can cause severe problems, such as in the brain.
If the tumor is cancerous, the outcome depends on the type and stage of the tumor at diagnosis. Some cancers can be cured. Some that are not curable can still be treated, and people can live for many years with the cancer. Still other tumors are quickly life threatening.
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, and the A.D.A.M. Editorial team.