Cancer is the uncontrolled growth of abnormal cells in the body. Cancerous cells are also called malignant cells.

Carcinoma; Malignant tumor

Cells are the building blocks of living things. Cancer grows out of normal cells in the body. Normal cells multiply when the body needs them, and die when the body doesn't. Cancer appears to occur when the growth of cells in the body is out of control and cells divide too rapidly. It can also occur when cells “forget” how to die.

There are many different kinds of cancers. Cancer can develop in almost any organ or tissue, such as the lung, colon, breast, skin, bones, or nerve tissue.

There are multiple causes of cancers, including:

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

However, the cause of many cancers remains unknown.

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

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

Certain cancers are more common in particular geographic areas. For example, in Japan, there are many cases of gastric cancer, while in the U.S. this type of cancer is relatively rare. Differences in diet may play a role.

Some other types of cancers include:

• Brain cancer
• Cervical cancer
• Uterine cancer
• Liver cancer
• Leukemia
• Hodgkin's lymphoma
• Non-Hodgkin's lymphoma
• Kidney cancer
• Ovarian cancer
• Skin cancer
• Testicular cancer
• Thyroid cancer

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. In some cancers, such as gallbladder cancer, symptoms often are not present until the disease has reached an advanced stage.

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
• 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.

A cancer diagnosis is difficult to cope with. It is important, however, that you discuss the type, size, and location of the cancer with your doctor upon diagnosis. You also will want to ask about treatment options, along with their benefits and risks.

It's a good idea to have someone with you at the doctor's office to help you get through the diagnosis. If you have trouble asking questions after hearing about your diagnosis, the person you bring with you can ask them for you.