Cancer ranks high on the list of diseases most feared by people everywhere, and with good reason.

At some point in their lives, cancer will affect one out of every two men and one out of every three women, according to the American Cancer Society (ACS). It is the second leading cause of death in the United States, after heart disease.

Cancer is the abnormal, uncontrolled growth of cells within the body. All cells are "programmed" to grow, divide, to perform certain functions and, eventually, to self-destruct. This programmed life cycle gets rid of old, damaged cells to make room for healthy cells.

When something goes wrong in the cell's genetic code, cells may continue to live past their normal lifespan, divide uncontrollably and be unable to perform their programmed function. Their presence can crowd out normal cells and they can spread to other parts of the body.

Understanding what causes cells to malfunction is a key to preventing cancer. Some risk factors that cause cancer simply cannot be prevented. These include having a family history of cancer and advancing age.

However, about 75 percent of cancers are believed to be at least partially related to lifestyle choices, according to the ACS. Changing habits and making healthier choices can help prevent many types of cancers.  

Avoiding smoking is perhaps the single greatest step a person can take to reduce cancer risk. Before the introduction of mass-produced cigarettes in the 20^th century, lung cancer was rarely diagnosed. Today, lung cancer is the leading cause of all cancer deaths and smoking causes 87 percent of lung cancer, according to the ACS.