Реферат: Cancer Essay Research Paper Cancer is a
Cancer Essay, Research Paper
Cancer is a word used to describe a group of diseases. Each has its own name, its own treatment, and its own chances of being cured. Each is different from the others in many ways, but every cancer, whatever its called or whatever part of the body it is located in, is a disease of the body?s cells. The millions of tiny cells that make up the human body are so small that they can be seen only by looking through a microscope. There are different kinds of cells, but they all make new cells by dividing into two. This is how worn-out, old cells are replaced with strong new ones. When a cell changes and doesn?t do the job it should do for the body, it divides into more cells like itself, then these cells keep dividing into more cells. A group of these cells is a tumor. There are two kinds of tumors. A benign tumor is not cancer. The cells of a benign tumor can crowd out healthy cells, but they cannot spread to other parts of the body. A malignant tumor is cancer. Like a benign tumor, it can take over other healthy cells around it, but it can also spread to other parts of the body. To do this, a cell or group of cells from the tumor breaks away and moves, usually though the blood, to other parts of the body. There they divide and start tumors made of malignant cells like the ones that made up the first tumor. When this happens, it is called metastasis. Skin cancer is the most prevalent of all cancers, and it?s increasingly common. About a million Americans will develop skin cancer this year. It is a disease in which cancer cells are found in the outer layers of skin. Skin protects the body against heat, light, infection, and injury. It also stores water, fat, and vitamin D. The skin has two main layers and several kinds of cells. The top layer of skin is called the epidermis. It contains three kinds of cells: flat, scaly cells on the surface called squamous cells, round cells called basal cells, and cells called melanocytes, which give skin its color. The inner layer of skin is called the dermis. This layer is thicker, and contains blood vessels, nerves, and sweat glands. The hair on skin also grows from tiny pockets in the dermis, called follicles. The dermis makes sweat, which helps cool the body, and oils that keep the skin from drying out. Skin cancer is viewed as an undeclared epidemic by dermatologists. “Skin cancer is now about as common as all other cancers combined,” says Martin A. Weinstock, M.D., Ph.D., director of Brown University?s Dermatoepidemiology Unit and Chief of Dermatology at the Providence Veteran?s Affairs Medical Center. He also says there?s no evidence the epidemic has peaked, which means it could get worse. Skin cancer is quite curable when treated early. More than ninety percent of skin cancers are completely cured. It?s also largely preventable, simply by avoiding sun and sunlamp exposure. Sunscreen is the most common defense against skin cancer. However, only two in five people consistently use sunscreen whenever they?re in the sun. Few people say they sunbathe, but about one in five adults still does. There are three main types of skin cancer. Melanoma is the least common but most serious because this killer is responsible for three-quarters of the nearly 10,000 skin cancer deaths per year. The other two types, basal cell and squamous cell carcinomas, are often referred to together as non-melanoma skin cancer. Basal cell cancer is by far the most common skin cancer, followed by squamous cell carcinoma, which can also become a killer. Between 1980 and 1989, the incidence of non-melanoma skin cancers increased sixty-five percent and melanoma twenty-one percent. Skin cancer is also striking at younger ages than before. One-quarter of the more than 30,000 people expected to develop melanoma this year will be thirty-nine or younger. Other kinds of cancers that may affect the skin include cutaneous T-cell lymphoma, a cancer of the lymph system, and Kaposi?s sarcoma. Melanoma is the fastest-growing type of cancer, affecting about 32,000 Americans in 1993. The skin cancer is triggered by UV rays from the sun and is signaled by the growth or appearance of an irregular more. If caught early, melanoma is completely curable with the mole?s removal. However, the cancer can and will spread if not caught early. Developing skin cancer is at least a two-step process, involving initiation and promotion of malignant growth. Studies have shown that UV harms a mechanism for repairing cell damage. Once the repair system is impaired, cells become increasingly vulnerable to injury. Subsequent UV exposures make it worse, and can initiate malignancy. After UV exposure, the repair mechanism normally directs damaged cells to commit suicide. That is why skin peels after a sunburn. However, previously damaged cells with a malfunctioning repair system escape this process. Genetic damage accumulates as normal cells die and abnormal ones survive. It?s been determined that skin does not have to be burned to be damaged, and such damage accumulates with chronic, everyday exposure. Two types of UV radiation reach the earth, UVA and UVB. Both contribute to skin damage, including skin cancer. There are no “safe” UV rays. But the SPF sunscreen numbering system was devised as a guide to protect against sunburn, which is caused mostly by UVB rays. Because sunscreens allow one to stay out in the sun longer without burning, exposure to UVA rays is increased, and many sunscreens don?t protect against these rays. While sunscreens protect against sunburn, they don?t necessarily prevent cancer. If one uses sunscreens to spend more time in the sun, the skin could collect about the same total exposure to damaging radiation. This is why it?s still a good idea to stay out of the sun at midday and to wear protective clothing and hats. Some studies estimate that diet may be involved in forty to sixty percent of all cancers. A high fat intake increased the likelihood of skin cancer after exposure to UV radiation, while switching to a low-fat diet after exposure reduced the incidence of skin cancer. The National Academy of Sciences recommends a diet in which thirty percent or less of the calories come from fat. The National Cancer Institute, the American Cancer Society, the American Heart Association, and other health organizations support this recommendation. Once cancer develops, early detection and treatment are the best defense. Those with blonde or red hair should be especially vigilant. Self-exams are recommended, and any growth, mole, or discoloration that appears suddenly or begins to change, or any sore that appears and doesn?t heal should be brought to a doctor?s attention. Characteristics of cancerous moles are asymmetry, ragged edges, bleeding, itching or pain. Skin cancer is more common in people with light colored skin who have spent a lot of time in the sunlight. Skin cancer can occur anywhere on the body, but it is most common in places that have been exposed to more sunlight, such as the face, neck, hands, and arms. Skin cancer can look many different ways. The most common sign of skin cancer is a change on the skin, such as a growth or a sore that won?t heal. Sometimes there may be a small lump. This lump can be smooth, shiny and waxy looking, or it can be red or reddish brown. Skin cancer may also appear as a flat red spot that is rough or scaly. Not all changes in the skin are cancer, but all changes should be brought to the attention of a doctor. For any type of skin cancer, treatment involves removing the lesion, usually in an outpatient procedure. The treatment goal is to remove or destroy the growth completely with as little damage as possible to healthy tissue. Doctors evaluate numerous factors in planning treatment. Considerations include type of cancer, tumor size and location, extent of disease, whether it?s new or recurrent, potential for scarring, and the patient?s overall health. Types of surgery include cryosurgery (destruction by freezing), laser surgery, and cuttrettage and electrodessication (using a spoon-like blade to scoop out the growth, followed by destruction of surrounding tissue with electric shock). Chemotherapy uses drugs to kill cancer cells. In treating skin cancer, chemotherapy is often given as a cream or lotion placed on the skin to kill cancer cells. Chemotherapy may also be taken by pill, or it may be put into the body by a needle in a vein or muscle. Chemotherapy given in this way is called a systemic treatment because the drug enters the bloodstream, travels through the body, and can kill cancer cells outside the skin. Biological therapy tries to get the body to fight cancer on its own. It uses materials made in the body or in a laboratory to boost, direct, or restore the body?s natural defenses against disease. Even after successful treatment, people who have had skin cancer remain at increased risk of developing it again. Protecting their skin from UV exposure is critical in helping to prevent a recurrence. It should become a life-long habit.