What is Cancer?

Author: Angela Thomas
Content Contributor: The Masterman School
Last Reviewed: October 31, 2001

Cancer is a general term for more than 100 diseases characterized by the uncontrolled , abnormal growth of cells in different parts of the body. Certain types of cancer can often spread to from one location to another. Cancer cells grow geometrically, meaning first there is one cancer cell, then two, then four, then eight and so on. Cancerous tumors are grouped into one of two categories, malignant or benign. Evidence of the existence of cancer can be dated back as far as prehistoric times. It has been found in the skeletons of prehistoric animals and even in Egyptian mummies. Cancer is classified into five major groups:


Carcinoma is a cancerous tumor originating in the epithelial system (surface tissue of body organs). Sometimes people develop carcinoma of unknown primary. This is when malignant cells are found somewhere in the body, but their origin, or the place where they first started growing, is unknown. Carcinoma is the most common form of cancer accounting for nearly 80% to 90% of all cases.


Sarcoma is a disease in which malignant tumors are found in the bone, cartilage, muscle, fibrous connective tissue, or fatty tissue. There are three main types of sarcomas including soft tissue, Kaposi's, and Ewing's. Soft tissue sarcomas develop in the muscles, fat, blood vessels, nerves, and synovial tissues (tissues around joints). Kaposi's sarcoma is found in the tissues under the skin or mucous membranes which line the mouth, nose, and anus. It causes red or purple lesions on the skin and spreads to other parts of the body. Ewing's sarcoma is a rare disease in which cancerous cells are found in the bone. It occurs most commonly in the pelvis, the thigh bone, the upper arm bone, or the ribs. Ewing's sarcoma is most often seen in teenagers.


Myeloma is the uncontrolled growth of plasma cells in the bone marrow. Plasma cells are a critical part of the body's immune system. They are manufactured in bone marrow and then move into the bloodstream. In most cases plasma cell tumors are monoclonal (originating from a single defective cell that began the cycle of uncontrolled cancerous growth).


Lymphoma is a cancerous tumor originating in the lymph system. The lymph system is a connecting network of glands and vessels which produce and circulate lymph through the body. Lymph is a colorless, watery fluid that contains white blood cells called lymphocytes. Along the vessels are organs called nodes. Lymph nodes are found in the neck, under the arms, in the groin and abdomen. Lymph nodes make and store infection fighting cells. When lymphoma occurs, cells in the lymphatic system grow abnormally. They divide to rapidly and grow without order or control. The cells are immature and do not die like a normal cell. They continue to divide as immature cells that cannot do their jobs well. Too much tissue is formed and tumors begin to grow. Because there is lymph tissue in many parts of the body, the cancer cells may spread to other parts of the body such as the liver or spleen or into the bone marrow. Lymphomas are divided into Hodgkin's and non-Hodgkin's lymphomas. They are distinguished by cell type and they share similar symptoms such as painless swelling of the lymph nodes, fever, and fatigue.


Leukemia is a malignant disorder of the body's blood forming tissue - mainly bone marrow, lymph nodes and spleen. In leukemia, the blood forming tissues flood the bloodstream and lymph system with immature white blood cells. The immature cells cannot fight infections. They reduce the production of normal red blood cells and tiny discs called platelets. Uncontrolled leukemia causes infections due to the lack of normal infection fighting white blood cells; severe anemia due to the lack of oxygen carrying red blood cells; and bruising and hemorrhaging, due to the lack of platelets. Leukemia is divided into two categories, acute and chronic. Acute affects immature white blood cells, progresses rapidly, and is most is often seen in children. Chronic leukemia occurs most frequently in adults and progresses slowly.

The study of cancerous tumors is called oncology. Doctors who specialize in the diagnosis and treatment of cancer are called oncologists.

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