Types of cancer

   Cancers are subdivided into two large classes: benign and malignant. Benign tumors,  as already mentioned, remain isolated from the surrounding tissues and grow within their own capsule. Although benign means harmless, the increasing size of these tumors may displace adjoining structures, and by placing pressure on adjacent tissues may sometimes cause damage. A fatty tumor called lipoma, which develops under the skin, causing a bump on the body's surface, belongs to this benign class.

   Malignant tumors

   Malignant tumors are composed of cells whose multiplication is out of control, and as they continue to multiply they send out tentacle like projections called processes that invade surrounding tissues. The invading growth often destroys these structures, usually by interfering with and appropriating their supply of blood. This may lead to bleeding and ulceration.

   Often these wildly-growing cells break away in small groups and, carried in the blood or lymph, travel to distant organs. Here they set up a beach-head, and, once established, develop into secondary tumors similar to the original one. This process of migration is called metastasis.  Metastatic tumors may endanger the victim's life even more than the original tumor.

   As a cancer develops in a particular part of the body, its cells more or less partake of the nature of the normal cells of the tissue or organ in which it originates. For this reason, the various kinds of cancer roughly parallel the various kinds of normal tissue in which a malignant tumor may grow. While there are numerous classes and subclasses of cancers, we will mention only four major types:

   Carcinomas. The largest group of cancers, known as carcinomas, originate from epithelial cells. Some of these cover the body's surfaces, such as the skin, Others line its tubes and cavities, such as the mucous membranes of the air passageways, intestines, bladder, and uterus. Still others compose the functioning cells of its glands, as in the salivary glands, the liver, pancreas, and prostate.

   Leukemias develop in the tissues that produce blood cells, such as the bone marrow and lymph nodes.

   Lymphomas develop from the cells of the lymph glands, as for example, the spleen and lymph nodes.

   Sarcomas arise in the body's supporting tissues bone, blood vessels, muscle, and fibrous tissue.