Lecture 10 Cancer Causes and Risk Factors Environmental The Role of Genes and Environment in Cancer Development Environment is 90 95 Genes is 5 10 Categories of Cancer Causes and Risk Factors Age Environmental Agents Lifestyle Factors Tobacco use Alcohol Use Diet Food Radiation Oncogenic Viruses Heredity Ultraviolet radiation 1 Alcohol 3 Occuptation 3 Pollution drugs additives 1 Tobacco 33 Diet 30 Ionization radiation 4 Infectious agents 9 Estimate of Cancer Deaths and their Environment Cause The Ames Test for Carcinogenic Potential Mutagenic able to cause a mutation Carcinogenic able to cause cancer Take bacteria that has a mutation that causes them to not be able to produce histidine and bacteria that can produce in a dish that does not have histidine Bacteria with mutation cannot grow Bacteria does grow Add liver homogenate and see if it will cause mutations and act like a carcinogen It allows the bacteria to produce hisitidine again Age and Cancer Risk Examples 60 79 years risk for colon cancer is 58X greater than someone who is 40 Lung cancer 165X at 60 79 than 40 Prostate cancer 2740X greater 60 79 than 40 Leukemia 4X greater 60 79 than 40 Geographical Differences in Cancer Prevalence Different cancers are much more common in different countries around the world Ex Prostate cancer is the highest in the U S while in Thailand the leading cancer type is liver cancer Environment vs Heredity Stomach cancer is extremely common in Japan while colon cancer is not In the U S stomach cancer is not very common while colon cancer is Environment vs Heredity Study of people that move from 1 country to another Heredity stays the same environment changes Stomach cancer high colon cancer low in Japan Opposite is true in U S Japanese immigrants move to U S Differences begin to disappear Children of immigrants acquire cancer risks of new location Thus environment plays a larger role than heredity 80 90 of cancer risk due to environment 10 20 due to heredity Cancer Related Deaths Across the Globe North America cancer deaths mainly from lung cancer maybe due to high rates of smoking Low death rates in Columbia and Venezuela may be due to dietary factors Uruguay has greatest mortality in South America and highest smoking rates Low cancer mortality due to high burden of infectious disease Low income and limited access to health care Chemicals and Cancer Risk Over the course of the century use of pesticides and plastics have increased There is an argument that since breast and colon cancer cases have not increased the chemical use and cancers are not related The exposure to the chemicals may not be in a high enough dose to be harmful or cause harmful effects People with higher metabolism could metabolize the chemicals fast enough so that they chemicals are not in their system for very long Cancer Deaths Linked to Diet Diet is 35 Lung cancer 20 Colorectal cancer 70 Pancreatic cancer 50 Prostate cancer 75 Gall bladder cancer 50 Other cancers 10 Gastric cancers 35 Breast cancer 50 Endometrial cancer 50 Larynx Bladder Mouth Pharnyx Esophagus 20 Diet and Cancer Risk Foods contain carcinogens and anti carcinogens Anti carcinogens in fruits may block carcinogens Epidemiologists estimate that diet plays a role in 30 of all fatal cancers Smoking and Lung Cancer Many unregulated carcinogens in cigarettes Very large increase in cigarette consumption While there was a large increase in male lung cancer deaths Smaller increase in female lung cancer deaths because women did not pick up smoking until later Dose Response Relationship Between Cigarette Smoking and Lung Cancer Age started smoking starting cigarettes in 20s has lower risk of cancer than someone who started when they were 15 Cigarettes per day More smoked greater the risk Depth of inhalation longer draws increases risk Interaction of Alcohol and Tobacco Smoke in Causing Mouth and Throat Cancer The risk is very high in a heavy drinker and heavy smoker Radiation and Cancer Gamma rays and X Rays Ionization radiation is high frequency radiation with enough energy to remove an electron from an atom ionize or molecule Ionization radiation has enough energy to damage the DNA in cells which in turn may lead to cancer Ultraviolet UV Rays High energy UV damages DNA whereas low energy UV does not Visible light Infrared rays Microwaves Radiofrequency radio waves Extremely low frequency ELF radiation Non ionization radiation is low fequency radiation that does not have enough energy to remove electrons or directly damage DNA Heredity and Cancer BRCA mutation increases the risk of cancer BRCA1 and BRCA2 are heritable mutations of DNA repair genes Ex Angelina Jolie had a double mastectomy because she tested positive for two genes that gave her an estimated 87 risk of breast cancer and 50 risk of ovarian cancer
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