Cancer

Cancer refers to disease caused by the malignant growth of a certain type of cells in vertebrates: epithelial cells. This growth usually results in a mass called a tumor, but also can involve a change in the composition of the blood or other body fluids such that a cancer is present but a tumor is not formed. Although the origin of cancer in an epithelial tissue is strictly required for the most technically accurate use of the term, cancer, the word is often used, even by physicians and hospitals, to include all the diseases directly caused by malignant tumors and cells. For example, malignant tumors called sarcomas arise from abnormal muscle-type cells, and since these tissues are derived from mesothelium rather than from epithelium, that word sarcoma is used rather than cancer to name the tumor. Still, cancer centers and specialists include treatment of sarcoma in practice, despite the fact that sarcomas and cancers differ in the medical classification of malignant tumors. In other words, all types of malignant tumors are sometimes referred to as cancers, and one type of these malignancies:epithelial malignancies, are, more strictly, also called cancers.

This introductory article will give a brief description of what a malignancy is, and how cells are thought to become malignant. That understanding is important as a basis to comprehending the medical and surgical treatment of cancers, and methods in their prevention. Important types of cancers (epithelial malignancies) are surveyed, with links provided for further information. The clinical emphasis is on human cancers, but references to cancers in other species of animals is also given a section. Although the frequencies and the aggresiveness of the various types of cancers vary according to species, generally, the basic biology of cancers is true for all species, including humans and domestic animals.