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Chapter 11

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Simon Fraser University
Biomedical Physio & Kines
BPK 140
Penny Deck

Chapter 11 What is Cancer? Cancer is the name given to a large group of diseases characterized by the uncontrolled growth and spread of abnormal cells. Under normal conditions, healthy cells are protected by the immune system as they perform their daily functions of growing, replicating, and repairing body organs. When something interrupts normal cell programming, uncontrolled growth and abnormal cellular development result in a new growth and abnormal cellular development result in a new growth of tissue. This new tissue serves no physiological function and is called a neoplasm. When this neoplasmic mass forms a clump of cells it is known as tumor. Not all tumours are malignant (cancerous); in fact, most are benign (non-cancerous). Benign tumours are harmless unless they grow to obstruct or crowd out normal tissues or organs. A benign tumour of the brain, for instance, is life-threatening when it grows and causes blood restriction resulting in a stroke. The only way to determine whether a given tumour is benign or malignant is through biopsy, or microscopic examination of cell development. Benign and malignant tumours differ in several key ways. Benign are generally ordinary-looking cells enclosed in a fibrous shell or capsule that prevents their spreading to other body areas. Malignant tumours are usually not enclosed in a protective capsule and can therefore spread to other organs. This process, known as metastasis, makes some forms of cancer particularly aggressive in their ability to overcome bodily defences. Metastasis is the process by which cancer spreads from one area different areas of the body. What Causes Cancer? Most research supports the idea that cancer is caused by external (chemicals, radiation, viruses, and lifestyle) , and internal (hormones, immune conditions, and inherited mutations) factors. One theory proposes that cancer results from spontaneous errors during cell reproduction. Another theory suggests that cancer is caused by some external agent or that enter a normal cell and initiates the cancerous process. Carcinogens are cancer-causing agents. A third theory came out of research on certain virus believed to cause tumours in animals. This research led to the discovery of oncogenes, which are suspected cancer-causing genes present on chromosomes. Proto-oncogenes are genes that become oncogenes under certain conditions. Oncologists are physicians who specialize in the treatment of malignancies. Risk for Cancer 1. Lifestyle Lifetime Risk refers to the probability that an individual, over the course of a lifetime, will develop cancer or die from it. Relative Risk is a measure of the strength of the relationship between risk factors and a particular cancer. Basically, relative risk compares your risk if you engage in certain known risk behaviours with that of someone who does not engage in such behaviours. Dietary intake, sedentary lifestyle, alcohol, cigarettes, stress, and other lifestyle factors seem to pay a role. Further confirming this theory is that colon and rectal cancer occur more frequently among persons with a high-fat, low-fibre dietary intake, in those who don’t eat enough fruits and vegetables, and those who are inactive. 2. Smoking Of all the potential risk factors for cancer, smoking is among the greatest. In developing countries, smoking is responsible for 80% of all deaths from lung cancer. Cancer can cause lung, pancreas, bladder, and kidney, the larynx, mouth, pharynx, esophagus, stomach, liver, and cervix cancers, which are directly related to long-term smoking. 3. Obesity Cancer is more common among people who are obese. Women with a high BMI have a higher mortality rate from breast, uterine, cervical, and ovarian cancers; men with a high BMI have higher death rates from prostate and stomach cancers. The risk of breast cancer increases, the risk of colon cancer in men increase; the risks of gallbladder and endometrial cancer increases. 4. Biological Factors Some research shows that cancers of the breast, stomach, colon, prostate, uterus, ovaries, and lungs do appear to have a heredity link. A woman has a much higher risk of developing breast cancer if her mother, sister, or daughter has the disease, particularly if they had it a young age. 5. Occupation and Environment Workplace hazards account for only a small percentage of all cancers. One of the most common occupational carcinogens is asbestos, insulation, and automobile industries. Nickel, chromate, and chemicals such as benzene, arsenic, and vinyl chloride have been shown to be carcinogens for humans. Also, people who work certain dyes and radioactive substances, or with herbicides and pesticides may have increased risk of cancer. Ionizing radiation – radiation from X-rays, radon, cosmic rays, and ultraviolet radiation (UV-B) is the only form of radiation linked to cancer. 6. Social and Psychological Factors People who are lonely, depressed, and lack social support are more susceptible to cancer than their mentally and emotionally healthy counterparts. Similarly, people under chronic stress and those with poor nutrition or sleep habits develop cancer at a slightly higher rate than the general population. Experts believe that severe depression or prolonged stress may reduce the activity of the body’s immune system, thereby wearing down bodily resistance to cancer. 7. Chemicals in Food Among the food additives suspected of causing cancer is sodium nitrate, a chemical used to preserve and give colour to red meat. Research indicates that the actual carcinogen is not sodium nitrate but nitrosamines substances formed when the body digests sodium nitrates. Clostridium botulinum, which is the cause of the highly virulent food-borne disease called botulism. There is also concern about the possible harm caused by pesticide and herbicide residues. 8. Infectious Diseases Infections are thought to influence cancer development in several ways, most commonly through chronic inflammation, suppression of the immune system, or chronic stimulation. Viruses such as hepatitis B (HBV) and C (HCV) are believed to stimulate cancer cells in the liver because they are chronic diseases that cause inflammation of liver tissue. Nearly 100% of women with cervical cancer have evidence of human papilloma virus (HPV) infection, believed to be a major cause of cervical cancer. HPV is a group of more than 100 different viruses of which 40 are transmitted through sexual activity. 9. Medical Factors Some medical treatments increase a person’s risk for cancer. One famous example is the widespread use of the prescription drug diethylstilbestrol (DES) to control problems with bleeding during pregnancy and to reduce the risk of miscarriage. Another example is the use of estrogen replacement therapy for postmenopausal women because of the potential risk of increased uterine cancer. Ironically, chemotherapy, which is used to treat cancer, may also increase risk of other forms of cancer. Types of Cancer The term cancer refers to hundreds of different diseases. Four broad classifications are made: 1. Carcinomas – Epithelial tissues (tissues covering body surfaces and lining most body cavities) are the most common sites for cancers. Carcinoma of the breast, lung, intestines, skin, and mouth are examples. These cancers affect the outer layer of the skin and mouth as well as the mucous membranes. They metastasize through the circulatory system initially and form solid tumours. 2. Sarcomas – sarcomas occur in the mesodermal, or middle, layers of tissue for example, in bones muscles, and general connective tissue. They metastasize primarily via blood in the early stages. These cancers are less common and also form solid tumours. 3. Lymphoma
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