www.soran.edu.iq What Is Cancer? Cancer is a class of diseases characterized by out- of-control cell growth. There are over 100 different types of cancer, and each is classified by the type of cell that is initially affected. Cancer harms the body when damaged cells divide uncontrollably to form lumps or masses of tissue called tumors (except in the case of leukemia where cancer prohibits normal blood function by abnormal cell division in the blood stream).
www.soran.edu.iq More dangerous, or malignant, tumors form when two things occur: 1.a cancerous cell manages to move throughout the body using the blood or lymph systems, destroying healthy tissue in a process called invasion 2.that cell manages to divide and grow, making new blood vessels to feed itself in a process called angiogenesis.
www.soran.edu.iq What causes cancer? Cancer is ultimately the result of cells that uncontrollably grow and do not die. Normal cells in the body follow an orderly path of growth, division, and death. Programmed cell death is called apoptosis, and when this process breaks down, cancer begins to form. Unlike regular cells, cancer cells do not experience programmatic death and instead continue to grow and divide. This leads to a mass of abnormal cells that grows out of control.
www.soran.edu.iq How is cancer classified? There are five broad groups that are used to classify cancer. 1)Carcinomas are characterized by cells that cover internal and external parts of the body such as lung, breast, and colon cancer. 2)Sarcomas are characterized by cells that are located in bone, cartilage, fat, connective tissue, muscle, and other supportive tissues. 3)Lymphomas are cancers that begin in the lymph nodes and immune system tissues. 4)Leukemias are cancers that begin in the bone marrow and often accumulate in the bloodstream. 5)Adenomas are cancers that arise in the thyroid, the pituitary gland, the adrenal gland, and other glandular tissues.
www.soran.edu.iq Carcinogens Carcinogens are a class of substances that are directly responsible for damaging DNA, promoting or aiding cancer. Tobacco, asbestos, arsenic, radiation such as gamma and x-rays, the sun, and compounds in car exhaust fumes are all examples of carcinogens. When our bodies are exposed to carcinogens, free radicals are formed that try to steal electrons from other molecules in the body. Theses free radicals damage cells and affect their ability to function normally.
www.soran.edu.iq What is a carcinogen? Some of these changes may be inherited from our parents, while others may be caused by outside exposures, which are often referred to as environmental factors. Environmental factors can include a wide range of exposures, such as: 1.Lifestyle factors (nutrition, tobacco use, physical activity, etc.) 2.Naturally occurring exposures (ultraviolet light, radon gas, infectious agents, etc.) 3.Medical treatments (chemotherapy, radiation, immune system- suppressing drugs, etc.) 4.Workplace exposures 5.Household exposures 6.Pollution
www.soran.edu.iq How do researchers determine if something is a carcinogen? Testing to see if something can cause cancer is often difficult. It is not ethical to test a substance by exposing people to it and seeing if they get cancer from it. That’s why scientists must use other types of tests, which may not always give clear answers. 1.Lab studies 2.Studies in people
www.soran.edu.iq Lab studies Although lab studies alone can't always predict if a substance will cause cancer in people, virtually all known human carcinogens that have been adequately tested also cause cancer in lab animals. In many cases, carcinogens are first found to cause cancer in lab animals and are later found to cause cancer in people. Most studies of potential carcinogens expose the lab animals to doses that are much higher than common human exposures. This is so that cancer risk can be detected in relatively small groups of animals. It is not always clear if the results from animal studies will be the same for people as they are normally exposed to a substance.
www.soran.edu.iq Studies in people Another important way to identify carcinogens is through epidemiologic studies, which look at human populations to determine which factors might be linked to cancer. These studies also provide useful information, but they have their limits. Humans do not live in a controlled environment. People are exposed to many substances at any given time, including those they encounter at work, school, or home; in the food they eat; and in the air they breathe. It's very unlikely they know exactly what they've been exposed to or that they would be able to remember all of their exposures if asked by a researcher. And there are usually many years (often decades) between exposure to a carcinogen and the development of cancer. Therefore, it can be very hard to definitely link any particular exposure to cancer.
www.soran.edu.iq Who determines how carcinogens are classified? Several agencies (national and international) are responsible for determining the cancer-causing potential of different substances. International Agency for Research on Cancer (IARC) National Toxicology Program (NTP) US Environmental Protection Agency (EPA) Other agencies and groups
www.soran.edu.iq International Agency for Research on Cancer The International Agency for Research on Cancer (IARC) is part of the World Health Organization (WHO). Its major goal is to identify causes of cancer. The most widely used system for classifying carcinogens comes from the IARC. In the past 30 years, the IARC has evaluated the cancer-causing potential of more than 900 likely candidates, placing them into one of the following groups: Group 1: Carcinogenic to humans Group 2A: Probably carcinogenic to humans Group 2B: Possibly carcinogenic to humans Group 3: Unclassifiable as to carcinogenicity in humans Group 4: Probably not carcinogenic to humans
www.soran.edu.iq Radiation Both Wilhelm Röntgen and Marie Curie died of cancer caused by radiation exposure during their experiments. Not all types of electromagnetic radiation are carcinogenic. Low-energy waves on the electromagnetic spectrum are generally not, including radio waves, microwave radiation, infrared radiation, and visible light. Higher-energy radiation, including ultraviolet radiation (present in sunlight), x-rays, and gamma radiation, generally is carcinogenic, if received in sufficient doses.
Carcinogens in prepared food Cooking food at high temperatures, for example broiling or barbecuing meats, can lead to the formation of minute quantities of many potent carcinogens that are comparable to those found in cigarette smoke (i.e., benzopyrene) (Zheng et al. 1998). Charring of food resembles coking and tobacco pyrolysis and produces similar carcinogens. There are several carcinogenic pyrolysis products, such as polynuclear aromatic hydrocarbons, which are converted by human enzymes into epoxides, which attach permanently to DNA. Pre-cooking meats in a microwave oven for 2-3 minutes before broiling shortens the time on the hot pan, which can help minimize the formation of these carcinogens.