The end result is a tumor, a mass of cells. A benign tumor is one that will not spread, or metastasize, to other parts of the body. It is considered noncancerous. A malignant tumor, on the other hand, can spread throughout the body and is considered cancerous. When malignant cells break away from the primary tumor and settle into another part of the body, the resulting new tumor is called either a metastasis or a secondary tumor.
Cancer often takes many years to develop.
The process typically begins with some disruption to the DNA of a cell, the genetic code that directs the life of the cell. Such disruptions can be caused by many things, such as diet, tobacco, sun exposure, or certain chemicals. Some cells will enter a precancerous phase, known as dysplasia. Some cells will also enter the state of carcinoma in situ, in which the cancer cells are restricted to a microscopic site and do not pose a great threat. Eventually, unless the body's own immune system takes care of the wayward cells, a tumor will develop.