CANCER
Introduction
Mechanism
Prevention
Treatments
New Developments
Implications
Introduction
Cancer is a human disease which is a current issue in our society. It is the second major cause of death in New Zealand (following heart disease). What concerns people is the lack of cures for this disease, and New Zealand lifestyles promotes many factors that increase cancer risk.
Mechanism
Cancer is not one but many different diseases. What all cancers have in common is that some of the cells in the body have become abnormal. The cells become out of control. Our body consists of billions of cells. Normally, the body’s cells divide in an orderly way, allowing your body to grow and to heal after and injury. Cancer is a multi-stage process where as people age, they accumulate more somatic cell mutations. Occasionally, for reasons not clearly understood, something goes wrong in one cell, causing it to get or give the wrong instructions. When this happens, the cell becomes abnormal. Normally, the immune system is constantly destroying mutated cells. However, if the mutated cell is not killed successfully, it starts dividing repeatedly in an uncontrolled way, forming a group of abnormal cells. These cells do not seem to know when to stop, and as they multiply they take up more room. These cells form a lump called a tumor. Tumors can be benign (not a cancer) or malignant (a cancer). Benign tumors do not spread to other parts of the body. Meanwhile, malignant tumors are cancers. Often, cancer cells break away from the original (primary) cancer and travel through the blood or lymph system to other parts of the body, where they may settle and form secondary cancers or metastases. For example, if breast cancer spreads to the bones, it is called a bone secondary rather than bone cancer. If not treated, malignant cells may cause death because they grow and spread so rapidly, and take up so much space and resources, which causes the normal surrounding cells to die off rapidly. However, some cancers, such as leukemia, the body’s blood-forming process becomes abnormal and an excess number of blood cells are formed. These abnormal cells do not cause tumors, though they are still cancer. Cancer cells resembles embryonic cells. They are unable to differentiate or mature into adult functioning state. The various forms of cancers are named accordingly to which part of the body it occurs in, eg breast cancer occurs in the breasts. There are more than 100 forms of cancer. Cancers can be grouped into three main categories. Carcinomas is a cancer which occur in the lining of the body’s external and internal surfaces, eg. the skin, mouth, and rectum. Examples include breast and skin cancer. Sarcomas is a cancer which form in connective tissues, eg muscles and bones. Lung cancer is one example. Leukaemias and lymphomas are cancers of the bone marrow and lymph glands.
Prevention
About 80 percent of cancers are potentially preventable. The current practices for prevention of cancer is to try and avoid carcinogens, or cancer causing agents, and do your best to live a healthy lifestyle. The most important carcinogen of cancer is cigarette smoking. Smoking causes 24% of all cancer deaths in New Zealand. About one in ten smokers die from lung cancer. UV rays are actually radiation rays from nuclear reactions in the sun, and this is also a carcinogen. Sun exposure and sunburn are the main cause of melanoma and other skin cancers. Hence, we should try to avoid sunbathing, sunburns, and tanning. Good nutrition helps in preventing cancer because what we eat plays a part in at least 1/3 of all cancers. Some food promote development of certain cancers, while some help protect against them. Fruits, vegetables, breads and cereals may help protect against certain cancers. Meanwhile too much fatty food increases the risks of cancer, and also means we are probably not getting enough of other foods. Physical activity helps keep your body a healthy weight which in turn may help protect you against some cancers. Alcohol is another carcinogen. It causes cancers of the mouth, throat, liver and esophagus. Being exposed to high concentrations of industrial hazards such as asbestos, benzene, formaldehyde, diesel exhaust, and radiation also causes cancers. Hence, these chemicals should be avoided. Certain infections and viruses also causes some cancers, but they are harder to avoid. Regular checkups would help a great deal as the cancer would not normally have enough time developing into a fatal degree without going unnoticed.
Treatments
Currently, there are three major practices for the treatment of cancer. Surgery is operated to remove cancer and any affected neighboring tissue. Surgery is carried out when there is a reasonable chance of removing all the cancer. Cancers close to vital organs cannot generally be removed surgically. Radiation therapy is the treatment of cancer by radiation. High-energy rays are used to kill cancer cells by preventing them from reproducing and spreading. Radiation may affect normal cells too, but they are able to repair themselves. Radiotherapy can be combined with surgery. Chemotherapy is the use of drugs to kill cancer cells. Because anti-cancer drugs enter the bloodstream and circulate through the body, they can kill cancer cells which have spread to distant parts of the body. Chemotherapy is often used in combination with surgery. Nearly all anti-cancer drugs work by interfering with DNA synthesis or function. In general, chemotherapy is best for treating cancers that are growing rapidly as they are more sensitive to chemotherapy. Because these drugs are so powerful, there are serious side effects such as hair loss and nausea.
New Developments
In the 20th century, technology is developing at an amazing rate, and people are gaining more knowledge about the ways to lead to a healthier life. There are now many researches going on to find ways of detecting and treating cancer more successfully. Some of these researches show signs of good prospects. About 5 to10 percent of cancers are inherited, and extensive research is being done to find the faulty genes responsible.
An ongoing research, called the Human Genome Project, which seeks to identify every gene in the human cell, will list the cancer susceptibility genes. This project is looking good as we have already identified many genes, eg BRCA1, BRCA2 are linked to some hereditary breast cancers. As knowledge about the immune system grows, scientists are devising ways, using the body’s own defenses, to attack cancer.
In the 1800’s, physicians noticed that tumors sometimes regressed in cancer patients who contracted bacterial infections. Later, a physician used vaccine of the dead bacteria on the site of the tumor, and brought about total regression of tumors in some individuals. One of the way the immune system can recognize differences among cells is by molecules, called antigens, that appear on the cell surface. Production of monoclonal antibodies is done by the immunization of mouse with human cancer to stimulate antibody production. The antibodies are produced are identical antibodies, or monoclonal antibodies. It is hoped that monoclonal antibodies would home on cancer cells by recognizing specific antigens, and trigger an immune attack that destroyed the target cells but ignored normal cells lacking cancer antigens. Many expected that these monoclonal antibodies could be made more deadly by loading them with toxic chemicals, and carry it directly to the tumors and thus kill the cancer cells. In clinical tests, human subjects generally mount an immune reaction that inactivates the injected mouse-derived molecules. In the meantime, workers are disguising the antibodies as something more resembling to human antibodies. The research of the monoclonal antibodies is still going on, and there are great rooms for greater developments. Either way, the treatment described above is considered a passive immunotherapy: the immune molecules are given to patients, who do not produce them on their own.
Meanwhile, a vaccine is an active immunotherapy because it rouses an immune response in the individual who needs protection. Subsequent studies showed that immune system cells known as T lymphocytes taken from immunized animals could transfer immunity against tumors to healthy animals of the same strain. And workers devised techniques to show that the T cells from the immunized mice could kill tumor cells grown in the test tubes as well.
During the past five years, improvements in medical imaging technology have enabled radiologists to take pictures of the body with unprecedented resolution and clarity. Meanwhile the rapid increase in available computer power has encouraged researchers to develop highly sophisticated techniques for displaying and analyzing those images. Two new technologies for cancer detection and therapy are three-dimensional multimodality display and computer-aided diagnosis. The displaying technique can fuse information from several imaging tools into a single coherent picture. In the second technique, software incorporating artificial intelligence and machine-vision algorithms can scan mammograms and chest x-rays and detect signs of cancer. There are three types of three-dimensional imaging that displays what cancer specialists require. CT scan, where bones appear bright and distinct, MRI, which is sensitive to tissues (and tumors), and PET, produces images of biological functions. However, as usual, the ultimate impact of the technology will not be seen for a decade or more.
New surgical techniques involving tiny incisions and special instruments that let surgeons see and operate deep within a patient’s body are becoming more frequently applied in cancer therapy. These methods should help spare some cancer patients the trauma of traditional surgery. The largest strides in cancer treatment will undoubtedly derive from advances in radiation therapy and chemotherapy that increase the effectiveness of these methods without causing permanent damage to healthy tissues. The removal of sections of cancerous bones rather than amputation are being studied as are bone marrow transplant techniques.
Implications
As more researches are done about cancer, more is discovered about cancer. The development of the knowledge of prevention and treatments of cancer have great implications with our society, socially and ethically. First of all, as more is known about the causes of cancer, we learn more about the relationship between cancer, lifestyle and culture. The death rate from cancer has fallen progressively in people under 50, probably because healthier habits and environment have reduced prolonged exposure to carcinogens. Traditionally, more men smoke than women, therefore incidence of lung cancer is the highest among the males. However, the figures are changing as the decreases in the number of smokers in some countries are starting to cause the cancer figures to decline. Unfortunately, the figures of female smokers are still increasing. Therefore, the number of women dying from lung cancer is still going up. Evidence from studies of populations that have migrated from one geographical area to another suggests that these variations are due to differences in lifestyle rather than ethnic origin, although lifestyle and heredity may interact. New Zealand lifestyles promotes many factors that increase cancer risk. The high meat and fat diet promotes breast and bowel cancers. High consumption of alcohol also increases risk of the cancer of the mouth, throat, liver and esophagus. The ozone thinning in the South Pole is the reason why New Zealand has the highest incidence of skin cancer in the world. Cancer is also an ethical issue in researches that is going on itself. Animal experimentation is already protested by anti-vivisectionists. Some complaints have been made with the use of human “guinea pigs”. There is scandal at the National Women’s Hospital over women with cervical cancer being denied treatment to see how their disease progressed, when compared to treated patients. Some people feel money is better spent on prevention education rather than on cures. Advertising campaigns are therefore made to provide these information. It is known by many that surgery to remove tumors may increase life “quantity” but may reduce “quality” of life. Cancer is also an biological issue. Many anti-cancer drugs themselves are suspected of being carcinogenic by being mutagenic. Children given chemotherapy for cancers such as leukemia have much higher cancer rates as adults.
(C)1999 by Yvonne Wang