Major Forms of Cancer - What is cancer?

Cancer would surely be easier to detect and treat if it were a single entity with a single simple cause. But it is not. Experts agree that there are actually some 100 different diseases that can be called cancers. They have different causes, originate in different tissues, develop for different reasons and in different ways, and demand vastly different kinds of treatment. All have one fatal element in common, however; in every case, normal cells have gone wild and lost their growth and development controls.

Normal cells, Malignant cells

Initial Stages

The cancer may start with just one or a few cells somewhere in the body that undergo a change and become malignant, or cancerous. The cells divide and reproduce themselves, and the cancer grows.

Most cancers arise on the surface of a tissue, such as the skin, the lining of the uterus, mouth, stomach, bowel, bladder, or bronchial tube in the lung, or inside a duct in the breast, prostate gland, or other site. Eventually, they grow from a microscopic clump to a visible mass, then begin to invade underlying tissues. As long as the cells remain in one mass, however, the cancer is localized.

Later Stages

At some later phase, in a process called metastasis , some of the cancer cells split off and are swept into the lymph channels or bloodstream to other parts of the body. They may be captured for a while in a nearby lymph node (a stage called regional involvement ), but unless the disease is arrested, it will rapidly invade the rest of the body, with death the almost certain result. Some cancers grow with a malevolent rapidity; some are dormant by comparison. Some respond to various therapies, such as radiation therapy; others do not. About half of the known types of cancer are incurable at any stage. Of the remaining half, it is obviously imperative to diagnose and treat them as early as possible.

How Cancers Are Classified

The cancers described above, arising in epithelial (covering or lining) tissue, are called carcinomas as a group. Another class of malignant tumors, similar in most basic respects, is the sarcomas , which originate in connective tissue, such as bones and muscles. A third group of cancers— leukemia and the lymphomas —includes diseases of the blood-forming organs and the lymphatic system, respectively, and does not produce tumors. They arise and spread in a basically different way.

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