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    How Cancer Develops

    Excerpted from
    Cancer Free: The Comprehensive Cancer Prevention Program
    By Sidney J. Winawer, M.D., Moshe Shike, M.D.

    Genes. Neoplasm. Metastasis. We know from experience that people's eyes sometimes glaze over at these and other scientific terms. But learning the basics of cancer's origins and progression is really quite easy, and it will help you to understand how the preventive measures outlined in this book work. Don't let the subject matter intimidate you; you needn't be a physician to comprehend cancer any more than you have to be a mechanic to drive a car.

    Cancer, named by the Greek physician Hippocrates around 400 B.C., encompasses a group of approximately 150 diseases that can arise anywhere on or within the body. All cancers share a critical characteristic, however: uncontrolled cell growth.

    A Brief (We Promise) Biology Lesson

    Cells are the basic units of biologic growth and development for all living organisms. Virtually all cells contain thousands of genes, imprints that determine every physical, biochemical and physiologic trait, from the color of your eyes to your ability to resist disease. These genes, made up of DNA (deoxyribonucleic acid), precisely program and control cell division. You inherit them from your parents and, in turn, pass them on to your children.

    Normally cells replicate themselves constantly: One cell becomes two, each with an identical genetic code; two become four; four, eight; eight, sixteen; and so on. As the new cells arise, the old ones die out. For reasons that are still not fully understood, about once every one million divisions, a daughter cell departs with an altered genetic code, or misprint.

    Dr. Peter Greenwald of the National Cancer Institute compares it to "copying an encyclopedia, which is more or less what's happening: You have all these DNAs replicating themselves. Mistakes can happen, and if they happen at a critical point that's severe enough to damage the DNA but not kill the cell, you've got a mutation."

    How Cancer Starts. Normally, cells replicate themselves in an orderly fashion. A malignant tumor develops when something goes awry, and poorly differentiated cells, such as those with disorganized nuclei in the lower illustration, grow without control.

    A defective gene doesn't necessarily lead to cancer; it increases vulnerability. The process that creates the defective gene is called an initiation, and the cause is called an initiator. Examples of initiators include cigarette smoking, x-rays and certain chemicals. A second element, a promoter, must act upon the initiated gene in order for the disease to occur.

    "Promoters," explains Dr. Daniel Nixon of the American Cancer Society, "make the cell-division process more active and disruptive, so that an initiated cell grows into a tumor." Alcohol, for instance, compounds the increased risk of mouth and throat cancers when combined with tobacco.

    Cancer develops when the tightly orchestrated structure and function of cell replication are disrupted by changes (mutations) that occur in the genetic material. Most normal cells carry several genes known as proto-oncogenes, a name derived from the Greek word onco, meaning mass or tumor. Usually they are considered allies of good health, fostering cell growth and division. Or they may exert no influence at all during the normal life of the cell. But under certain conditions, proto-oncogenes can be activated and changed into oncogenes that mediate the conversion of normal cells to cancer cells. Once again, carcinogens such as the ones mentioned above are often responsible for the transformation.

    Viewed under a microscope, cancer cells appear distinctly different from their normal counterparts:

    • Normal cells are round and have clearly defined cell membranes.

    • Normal cells grow only to the limits of their own defined space and architecture and then stop.

    • Normal cells have a nucleus with 23 sets of chromosomes, biologic units that bear the DNA.

    • Cancer cells possess irregular shapes and borders.

    • Cancer cells squeeze out other cells, invading neighboring and distant tissues and organs.

    • Cancer cells often have an enlarged nucleus that may contain a shortage or surplus of chromosomes or abnormal genes.

    What's more, whereas a healthy cell grows and divides systematically, a cancer cell multiplies rapidly and recklessly until the errant cells infiltrate and destroy the normal cells and tissues. Unless apprehended, the cancer will continue to spread, damaging healthy organs, interfering with body systems and possibly causing death.

    Even after the initial events produce a cancerous cell, the disease must still elude various defense and repair mechanisms to gain a foothold. The body's immune system is usually able to ferret out and dispose of roving cancer cells before they can spread or form a tumor. There are also defenses that prevent one or a few cancerous cells from developing into a significant cancer, although little is known about them at present.

    "We know of situations where people have occult cancers that never become clinically significant," says Dr. Peter Greenwald of the National Cancer Institute. (An occult cancer is one too tiny to produce symptoms or to be seen without microscopically examining the tissue.) "That's very common in the prostate, for example, and it undoubtedly occurs in the breast and other organs as well." Except for extremely rare cancers, it takes more than one mutation, or change, in one gene for a normal cell to progress all the way into a cancer cell.

    From scientific studies, it appears that the immune response to cancer may generally resemble the assault against bacteria and viruses, although the specific mechanism in cancer is unknown, and may, in fact, be quite different.

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