Tuesday, June 28, 2011

Cancer Causes controversies- Introduction


Part I: Risk Factors for Commonly Diagnosed Cancer Diseases 1
1. Bladder Cancer 3
2. Brain Cancer 9
3. Breast Cancer 19
4. Cervical Cancer 25
5. Colorectal Cancer 31
6. Esophageal Cancer 37
7. Gastric Cancer 45
8. Head and Neck Cancer 49
9. Leukemia and Lymphoma 55
10. Liver Cancer 65
11. Lung Cancer 73
12. Ovarian and Endometrial Cancers 83
13. Pancreatic Cancer 89
14. Prostate Cancer 95
15. Skin Cancer 101
16. Occupation-Associated Cancer 109

Part II: Behaviors and Controversies 113
17. Nutrition and Cancer 115
18. Body Weight and Cancer 127
19. Immune System and Cancer Risk 141
20. Controversies Concerning Cancer Screenings Benefits and Disadvantages
21. Controversies Surrounding Dietary Supplements and Foods for Cancer Prevention
22. Controversies Regarding Commonly Perceived Risk Factors and Cancer
23. Conclusion


Cancer’s mysteries and miseries have been with us for thousands of years. One of the earliest known references to this collection of diseases appears in ancient Egyptian papyri1·medical texts dating from about 1600 b.c. The ancient texts authors describe swellings and ulcerations that fail to heal, much like cancers we know today.
Little was learned about the nature of cancer during the following 1,500 years. But diagnostic procedures had by the year 1775 advanced enough to enable the English physician Dr. Percival Pott, of St. Bartholomew’s Hospital in London, to correlate the development of a specific cancer with prolonged exposure to a workplace toxin. At that time in England, it was common to employ small boys to sweep and clean the insides of chimneys- a treacherous occupation in itself.
In later years, the men who held this job as children experienced a high incidence of scrotal cancer. The doctor discovered that most of his patients with scrotal cancer had worked as chimney sweeps as children and had experienced prolonged exposure to the irritating effects of the soot. This was the first recognized and recorded instance of an occupational cancer due to environmental influences.
But it wasn’t until the early 20th century that science began to make great strides in understanding the causes of cancer.2 This includes the first epidemiological study that linked sunlight to skin cancer in 1907.2 In 1916 researchers learned that removing the ovaries from a strain of female mice with a high incidence of spontaneous breast cancer decreased the rodents’ risk of breast tumors. Later work showed that transplanting ovaries into male mice induced mammary tumors, supporting the theory that hormones in the ovaries could promote breast tumors.
In 1928 scientists identified cervical cancer cells in smears of exfoliated vaginal cells. This discovery led to the development of the Pap smear in 1960, now widely accepted as an effective method of preventing and screening for cervical cancer. Since then, other screening methods for the early detection of various cancers have become routine, such as colonoscopy for colorectal cancer and mammography for breast cancer. U.S. researcher Dr. Charles B. Huggins made a significant discovery in 1941 when he demonstrated that prostate cancer is hormone dependent. His research showed that physically castrating dogs that had metastatic prostate cancer reduced their disease burden, while injecting male hormones into dogs increased prostate cancer metastasis. Perhaps the single most important discovery was the identification of deoxyribonucleic acid (DNA) in 1944 as hereditary material. This opened up a whole new realm of science, leading researchers to determine that most carcinogens, agents that cause cancer, do so by damaging DNA or creating DNA mutations.
Since the 1970s, the United States and other parts of the world have taken an aggressive stance against cancer in medical laboratories. This has led to the development of therapeutic treatments such as the antiestrogen drug tamoxifen in 1977. Still used today to treat some types of breast cancer, more than 500,000 people have survived the disease because of this drug. However, the wider use of tamoxifen has been hampered by side effects. In another example, researchers linked prostate cancer with levels of prostate specific antigen (PSA), leading to the creation of the first routine protein biomarker test used in cancer screening and prevention in 1980. Nowadays, several tests screen for the early detection of cancer ·a key to successfully treating the disease.
Scientists soon learned that certain bacterial or viral infections could cause cancer. Researchers identified the bacterium Helicobacter pylori as a causative agent for stomach ulcer in 1982; it is now known that chronic inflammation caused by this bacterium is a major risk factor for stomach cancer. The human papillomavirus was found to be the causative agent of cervical cancer in 1983. Scientists followed up in 2004 by designing vaccines against the most common tumor-producing (oncogenic) human papillomavirus types, HPV16 and HPV18. It’s thought the vaccine could prevent up to 70 percent of cervical cancer cases worldwide. The completion of the Human Genome Project in 2000 means a great deal to cancer research. As every nucleotide of the human genome has been sequenced and mapped, the way is clear for scientists to learn how cancer cells are different from normal cells. This undoubtedly will lead to understanding individual variations at the DNA level, and it may help explain differences in disease susceptibility. Ultimately, more powerful and specific pharmaceutical drugs could be designed///////////////////////////////

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