Cancer occurs after a single cell in a tissue is progressively genetically damaged to produce a cancer stem cell possessing a malignant. These cancer stem cells are able to be uncontrolled abnormal. This serves to increase the total number of cancer cells at that location. The area of cancer cells at the base site becomes clinically detectable; it is called a primary tumor. Some cancer cells acquire the ability to penetrate surrounding normal tissues in the local area, forming a new tumor.