Cancer is a group of more than 100 different diseases. It can develop almost anywhere in the body. In brief, cancer can be defined as a condition where the normal cells of the body become abnormal and start growing and multiplying uncontrollably and gain the ability to spread throughout the body. In the normal state of the body, cells of the body need to divide to replace cells which are lost in day to day activities. For example, old cells in the intestine die and are lost in faeces. To replace these cells, new cells are created by the division of old cells. The division of these cells is tighly controlled by the body so that only as many cells are created as are needed for normal functioning of the body.
Cells are the basic units that make up the human body. Cells grow and divide to make new cells as the body needs them. Usually, cells die when they get too old or damaged. Then, new cells take their place.
Cancer begins when genetic changes interfere with this orderly process. Cells start to grow uncontrollably. These cells may form a mass called a tumor. A tumor can be cancerous or benign. A cancerous tumor is malignant, meaning it can grow and spread to other parts of the body. A benign tumor means the tumor can grow but will not spread.
Some types of cancer do not form a tumor. These include leukemias, most types of lymphoma, and myeloma.