Cancer involves the uncontrolled growth of abnormal cells that have mutated from normal tissues. This growth can kill when these cells prevent normal function of vital organs or spread throughout the body, damaging essential systems.

There are at least 200 different kinds of cancers. They can develop in almost any organ, fluid, or tissue. Some cancers affect blood cells, some affect skin; others affect bone, muscle, or nerve tissue.

In general, cancer appears to be caused by abnormal regulation of cell growth. Typically, the growth of cells in the body is strictly controlled -- new cells are made as needed to replace older ones or to perform needed functions. Cells die when they become damaged and/or are no longer needed. If the balance of cell growth and death is disturbed, cancer may occur.

Problems in the regulation of cell growth can be caused by abnormalities of the immune system, which normally would detect and stop aberrant growth. Other potential causes of cancer include the following

• Radiation
• Sunlight
• Tobacco
• Certain viruses
• Benzene
• Certain poisonous mushrooms and aflatoxins (a poison produced by organisms that can grow on peanut plants)

The three most common cancers in men in the U.S. are prostate cancer, lung cancer, and colon cancer. In women here, the three most frequently occurring cancers are breast cancer, lung cancer, and colon cancer.

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

Certain cancers are more common in particular geographic regions. For example, in Japan, there are many cases of gastric cancer while in the US this type of cancer is relatively rare. Dietary differences may account for the variance.

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

Some cancers may not have any symptoms at all. However, the following symptoms are common with most cancers:

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

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

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

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 undergo CT scans to determine the exact location of the tumor or tumors.

Treatment also 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.

• If the cancer is confined to one location and has not spread, the goal for treatment would be surgery 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, chemotherapy, or both. Some cancers require a combination of surgery, radiation, and chemotherapy.

The diagnosis of cancer often causes a lot of anxiety and can affect one's entire life. There are numerous support groups for cancer patients.

Although some research suggests that support group participation can increase survival time, other studies have not replicated this, so patients should decide whether to use support groups depending on their own needs and preferences.

Avoidance or cessation of tobacco products such as cigarettes is one of the best ways to prevent cancer. Many cancers can be prevented by avoiding other risk factors such as excessive exposure to sunlight and heavy drinking.

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