In general, tumors appear to be caused by abnormal regulation of cell growth. Typically, the growth of cells in the body is strictly controlled -- new cells are created to replace older ones or to perform new functions. If the balance of cell growth and death is disturbed, a tumor may form. Abnormalities of the immune system, which usually detects and blocks aberrant growth, can lead to tumors. Other causes include radiation, genetic abnormalities, certain viruses, sunlight, tobacco, benzene, certain poisonous mushrooms, and aflatoxins.

Tumors are classified as either benign (slow-growing and usually harmless depending on the location), malignant (fast-growing and likely to spread and damage other organs or systems) or intermediate (a mixture of benign and malignant cells).

Some tumors are more common in men than in women, some are more common amongst children or elderly people and some vary with diet, environment and genetic risk factors.

Symptoms depend on the type and location of the tumor. For example, lung tumors can cause coughing, shortness of breath or chest pain while tumors of the colon can cause weight loss, diarrhea, constipation and blood in the stool. Some tumors produce no symptoms, but symptoms that often accompany tumors include:

• fevers
• chills
• night sweats
• weight loss
• loss of appetite
• fatigue
• malaise

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 benign or 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 to determine the exact location of the tumor and its extent.

Common tests to most patients with tumors include:

• CT scan of the chest, abdomen, and pelvis
• Complete blood count
• Blood chemistries
• Biopsy of the tumor
• Bone marrow biopsy (for lymphoma or leukemia)
• Chest X-ray

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 disturb the proper functioning of the organ, sometimes no treatment is needed. Sometimes benign tumors may be removed for cosmetic reasons.

If a tumor is malignant, treatments include surgery, radiation, chemotherapy or a combination of these methods.

If the cancer is confined to one location, the goal of treatment is surgical removal of the tumor and cure. This is often the case with skin cancers. 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

Prognosis varies widely among different types of tumor. If the tumor is benign, the prognosis is generally very good. There are some instances where a benign tumor can cause significant problems, however (e.g., in the brain).

If the tumor is malignant, the outcome varies depending on the stage of the tumor at diagnosis. Some cancers can be cured, some that are not curable can still be treated well and patients can live for many years with the cancer. Still other tumors are rapidly fatal.