A tumor is an abnormal growth of body tissue. Tumors can be cancerous (malignant) or non-cancerous (benign).

In general, tumors appear to occur when there is a problem with the dividing of cells in the body. Typically, the division of cells in the body is strictly controlled. 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 division 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 causes include:

• Benzene and other chemicals and toxins
• Drinking excess alcohol
• Excessive sunlight exposure
• Genetic problems
• Inactivity (sedentary lifestyle)
• Obesity
• Radiation

Certain viruses can play a role in the development of tumors, such as cervical cancer (human papillomavirus) and hepatocellular carcinoma (hepatitis B virus).

Some tumors are more common in one gender than the other. Some are more common among children or the elderly. Others vary with diet, environment, and your 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, while tumors of the colon can cause weight loss, diarrhea, constipation, iron deficiency anemia, and blood in the stool.

Some tumors produce no symptoms, but symptoms that may occur with tumors include:

• Chills
• Fatigue
• Fever
• Loss of appetite
• Malaise
• Night sweats
• Weight loss

Like the symptoms, the signs of tumors vary based on their site and type.

When a tumor is found, a biopsy is performed to determine if the tumor is non-cancerous (benign) or cancerous (malignant). Depending on the location of the tumor, the biopsy may be a simple procedure or a serious operation.

Most patients with tumors undergo CT scans or MRI to determine the exact location of the tumor and how far it has spread. More recently, positron emission tomography (PET) scans have been used to find certain tumor types.

Other tests include:

• Biopsy of the tumor
• Blood chemistries
• Bone marrow biopsy (most often for lymphoma or leukemia)
• Chest x-ray
• Complete blood count (CBC)

Treatment also varies based on the type of tumor, whether it is benign or malignant, and its location. If the tumor is benign (meaning it has no potential to spread) and is located in a "safe" area where it will not cause symptoms or affect the function of the organ, sometimes no treatment is needed.

Sometimes benign tumors may be removed for cosmetic reasons, however. Benign tumors of the brain may be removed because of their location or harmful effect on the surrounding normal brain tissue.

If a tumor is malignant, treatments include:

• Surgery
• Radiation
• Chemotherapy
• A combination of these methods

If the cancer is in one location, the goal of treatment is usually to remove the tumor with surgery. If the tumor has spread to local lymph nodes only, sometimes these can also be removed. If all of the cancer cannot be removed with surgery, the options for treatment include radiation and chemotherapy, or both. Some patients require a combination of surgery, radiation and chemotherapy.

However, lymphoma is rarely treated with surgery. Chemotherapy and radiation therapy are most often used for treating lymphoma.

The diagnosis of cancer often causes a lot of anxiety and can affect a patient's entire life. There are many resources for cancer patients (see cancer resources).

The outlook varies widely among different types of tumors. If the tumor is benign, the outlook is generally very good. However, there are some instances where a benign tumor can cause significant problems, for instance, in the brain.

If the tumor is malignant, the outcome depends on the stage of the tumor at diagnosis. Some cancers can be cured. Some that are not curable can still be treated and patients can live for many years with the cancer. Still other tumors are quickly life-threatening.

Complications can occur if a tumor is located in a region of the body where it affects the function of the normal organ. If the tumor is malignant, it can also cause complications if it spreads (metastasizes).

Call your health care provider if you notice any suspicious lumps or bumps on your body, or if you notice a new or changing mole on your skin.

You can reduce the risk of cancerous (malignant) tumors by:

• Eating a healthy diet
• Exercising regularly
• Limiting alcohol
• Maintaining a healthy weight
• Minimizing exposure to radiation and toxic chemicals
• Not smoking or chewing tobacco
• Reducing sun exposure if you burn easily