Cancer is a deregulated multiplication of cells with the consequence of an abnormal increase of the cell number in particular organs. Initial stages of the developing cancer are usually confined to the organ of origin whereas advanced cancers grow beyond the tissue of origin. Advanced cancers invade the surrounding tissues that are initially connected to the primary cancer. At a later stage, they are distributed via the hematopoetic and lymphatic systems throughout the body where they can colonize in distant tissues and form metastasis. The development of cancers is thought to result from the damage of the cellular genome, either due to random endogenous mechanisms or caused by environmental influences.
The origin of cancers can be traced back to alterations of cellular genes. Genetic damage can be of different sorts: