What Is Cancer?
Basic information on how cancer develops, spreads, and is treated.

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image of woman doctor looking into microscope What Is Cancer?

When someone tells you about a friend or family member having cancer, they often use the words, "He has cancer." Yet, cancer isn't just one disease. In fact, there are hundreds of different types of cancers, and each kind can originate in any cell or organ in the body. All cancers have one thing in common - abnormal, uncontrolled cell growth.

Normally, cells grow and divide in an orderly fashion, involving a cycle to produce more cells only when the body needs them. This is a normal and healthy body process. But sometimes, cells keep dividing when new cells are not needed. These extra cells form a mass of tissue, called a growth or tumor.

Tumors can be benign or malignant:

  • Benign tumors are not cancerous. They can often be removed and, in most cases, they don't come back. Cells from benign tumors do not spread to other parts of the body. Most important, most benign tumors are not a threat to your life.
  • Malignant tumors, though, are cancerous. They are made up of abnormal cells that divide without control or order. They invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumor and enter the lymphatic vessels or bloodstream. That is how cancer spreads from the original cancer site to form new tumors in other organs. The spread of cancer is called metastasis.

When cancer spreads from its original location to another part of the body, the new tumor has the same kind of abnormal cells. It is considered the same cancer type as the primary tumor, but it often has new genetic changes. For example, if lung cancer spreads to the brain, the cancer cells in the brain are actually lung cancer cells. Then the disease is called metastatic lung cancer.

Forms of cancer
Cancers are named for the body tissues where they start. These are the main types of cancer.

  • Sarcomas are found in fibrous or soft tissues, such as muscles, bone or blood vessels.
  • Carcinomas are found in the epithelium. This is a layer of cells that covers the body surface and lines body organs, such as the breast, colon and lung.
  • Leukemias are cancers that start in blood-forming tissue, such as the bone marrow.
  • Lymphoma and myeloma are cancers that begin in the cells of the immune system.
  • Central nervous system cancers start in the tissues of the brain and spinal cord.

Cancer can develop at almost any stage in life. There are some types of cancer that develop in early childhood, such as retinoblastoma (a cancer of the eye). Others tend to develop in childhood, such as various forms of leukemia. And, of course, there are many forms that develop during adulthood, such as breast, colon and prostate cancers.

Cancer growth
It can take a year or many years before a growing tumor (benign or malignant) can be detected, either on physical examination or on an x-ray or other test. Each form of cancer has its own growth rate.

A cancer that is "in situ carcinoma" - which in Latin means "in place" - refers to a cancer that is found only in the place where it first formed and has not spread. Cancer or a "carcinoma" that is "in situ" may never develop further. But because it may grow and become invasive and malignant, it is usually removed surgically, if possible.

Some cancers remain "in situ" or localized, while other cancers are "regional", invading adjacent body organs. Other cancers may metastasize (spread) into the bloodstream (vessels) or lymphatic vessels, where they are carried through the body to a distant site or sites.

Treating cancer
There are different ways of treating cancer - mainly with surgery, radiation and/or chemotherapy. Because there are so many different types of cancer, research so far hasn't found a single cause or single cure for cancer. Yet, due to improved diagnosis and newer cancer treatments, doctors are curing more cancers every day and improving the survival rates for most types of cancers.

By Nancy Reid, Staff Writer
Created on 02/11/2002
Updated on 05/19/2010
Sources:
  • National Cancer Institute. Defining cancer.
  • American Cancer Society. Detailed guide: cancer (general information).
Copyright © OptumHealth.
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