Cancer is a common name given for a group of diseases characterised by uncontrolled production of abnormal cells. Cancer starts when the cells of an organ or tissue in our body grow and multiply out of control and form a mass, called a tumour.
Cell division is the basis of human life. Human body is made up of several organs like brain, lung, liver, stomach etc and each organ is made up of cells. Organs and tissues are constituted by cells characteristic of that organ. Cells divide for growth of an organ, for repairing tissue damage and to maintain functions of the organ. The divided cells are the exact replica of the parent cell.
Sometimes due to some faulty mechanism or due to factors which are not yet known, the daughter cells are abnormal i.e., their structure is not the same as that of the parent cells. These malignant cells cannot carry on the functions that normal cells can but require the same nutrition as normal cells. These cells start dividing and thus a large number of abnormal cells are produced. As a result of the proliferation of abnormal cells the body organs do not function normally and the person's nutrition is impaired. These cells cluster to form lumps, swellings, and sometimes produce ulcers in the respective organs and are called cancer. In case of blood cancers (leukaemia) the abnormal cells are in circulation throughout the blood stream and therefore no visible lumps or swellings are observed.
Another important fact in spread of cancer is that the cancer cells can separate itself from the tissue or organ of origin and spread to other parts of the body through lymphatic channels or blood vessels. Scientifically this process is known as metastasis and because of this unique characteristic, cancer is difficult to cure.