Treating cancer properly depends on defining each and every tumor very precisely. All kinds of characteristics are taken into account when coming up with this definition, but all these characteristics essentially fit into three broad categories. The three key questions that have to be answered are: where is the tumor growing, how fast is it growing, and how big has it already grown?
The first of these questions is critical because, again, cancers that develop in different tissues tend to behave differently. There are generally three types of malignant tumors, which develop in the three kinds of tissues.
Carcinomas These develop in the tissues that cover the surface of or line intemal organs and passageways (epithelium). Most epithelial cancers—carcinomas—develop in an organ that secretes something. For example, lung tissue secretes mucus, breast tissue secretes milk, and the pancreas secretes digestive juices.
Sarcomas These are soft tissue or bone tumors. They develop in any supporting or connective tissues—muscles, bones, nerves, tendons or blood vessels. Since supporting or connective tissue is found throughout the body, sarcomas can be found anywhere.
The same organ that develops a carcinoma can also develop a sarcoma, since the organ also has connective tissue in it. There are blood vessels in the pancreas, for example, and if a cell in the wall of the blood vessel develops a tumor, the tumor is a sarcoma even though it's in the pancreas.
