The Big Bad C
By Rear Adm. Joyce Johnson, D.O., M.A.

No one likes to talk about it, but everyone fears it. Rear Adm. Joyce Johnson, D.O., discusses what cancer is, how it spreads, and what factors could put you at risk.

Our body is made of constantly dividing living cells. Cell division is regulated by a complex series of controlled biological reactions. When the process loses its normal controls, cells can divide aggressively, and cancer can result. At the individual cellular level, the change from a normal cell to a cancerous cell is common. Usually, the body’s immune system recognizes a single cancer cell as foreign and attacks it. Sometimes, though, a cancerous cell is not destroyed, and it grows and multiplies, becoming a tumor. Some cancers can grow for years and still be small and asymptomatic; others are more aggressive, growing more quickly and spreading (metastasizing) more easily.

Cancer can metastasize in three ways:

• Lateral extension. As it grows, a tumor can invade adjacent spaces. For example, a bowel tumor can grow quite large before it has any symptoms or is diagnosed. By the time it is detected, it might have spread to surrounding tissues.
   
• Through the bloodstream. One or more cells from a primary tumor get into the bloodstream; the blood takes the cells to other organs where they are deposited and grow. Many tumors spread to the brain and liver via this route, because both organs have large blood supplies.
   
• Via the lymph nodes. Cancer cells move from a tumor into the lymph, and from the lymphatic system to other organs. Breast cancer frequently spreads from one breast to the other this way.

The way cancer spreads affects cancer recurrence and the effectiveness of treatment. Even if a large tumor mass is removed, microscopic tumor cells can remain in the body; over time, they can grow and become another tumor. For this reason, surgery might be followed by chemotherapy or radiation to kill any remaining cancer cells.

When a tumor in one location spreads and grows in another location, the secondary tumor will look similar to the primary tumor under a microscope. (For example, when lung cancer spreads to the liver, tissue from the cancer in the liver will resemble tissue from the cancer in the lung.)

No one is certain why some people get cancer and others don’t, but several risk factors for cancer have been identified. Some cancers, such as certain bowel and breast cancers, have a strong genetic link. Other cancers are caused by environmental contaminants—for example, lung cancers are related to asbestos and smoking. People with infectious diseases such as chronic hepatitis B and C are at greater risk for liver cancer. Those with suppressed immune systems (from steroids, HIV/AIDS, or other causes) have greater susceptibility to many cancers. Irradiation is another contributor; diet and nutrition also can have an impact.