Cancer is a set of diseases defined by out-of-control cell growth. It is a group of more than 100 diseases in which cells in a part of the body start to grow uncontrollably. There are many types of cancer which are categorized by the type of cell which is initially affected.

The human body is made of hundreds of millions of cells that grow, divide as well as die in an orderly fashion.  The normal cells divide faster during the early years of a person's life to allow him to grow. When the person becomes mature, most cells divide to replace dying or worn-out cells or to repair injuries.

Cancer cell growth is different from the growth of normal cells. The cancer cells continue to grow and form new and abnormal cells, instead of dying. They can also invade other tissues, something which normal cells cannot do. Invading other tissues and growing out of control makes a cell a cancer cell.

When damaged cells divide within the body to form masses of tissue or lumps called as tumors, cancer becomes harmful for the body. The tumors can grow and intervene with the nervous, digestive, and circulatory systems. They have an ability to release hormones which alter body functions. Tumors which stay in one place and shows limited growth are mostly considered to be benign.

There are different types of cancers. No matter where a cancer may spread, it is called by the place from where it started. For example, prostate cancer which has spread to the bone is called is metastatic prostate cancer and not bone cancer. Similarly, breast cancer which has spread to the liver is called as breast cancer and not liver cancer. Each type of cancer behaves differently. They grow at different rates and respond to different treatments. Hence, people need cancer treatment which is aimed at their particular kind of cancer.

Today, millions of people have had cancer or are living with cancer. However, the risk of developing most types of cancer can be reduced by changes in the lifestyle of a person. Eating a better diet, quitting smoking, being physically active, and limiting time in the sun are some of the ways to reduce the risk of cancer. The sooner a cancer is found as well as treated, the higher the chances are for living for many years.