Causes of Cancer |
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Many causes of cancers are known. For example, it is now accepted by many medical authorities, that excessive cigarette smoking is the major cause of lung cancer. Other countries in which cigarette smoking is widespread have had an equal or even a greater increase in lung cancer deaths. Excessive smoking is also believed to be implicated in cancers of the bladder, mouth, throat and larynx. Other cancers are caused by certain dyes and other chemicals, heavy metals, and overexposure to x-rays and sunlight. The first environmental cause of cancer was discovered by a British doctor in the 19th century. He found that cancer of scrotum in London's chimney sweeps was caused by the soot that lodged in the skin of the scrotum. Ever since 1940, when Dr. Francisco Duran of Yale University stated his belief that some human cancers were caused by viruses, an increasing amount of work in this field has tended to lend weight to this theory. Although no human cancer viruses have yet been isolated, viruses that cause different cancers in mice, hamsters, chickens, and rabbits have been found. Dr. Charlotte Friend of the Sloan-Kettering Institute in New York City has discovered a virus that causes leukemia in mice. Using this virus, mice have been immunized against leukemia, or cancer of the blood, with some degree of success. This limited success in the field of animal experimentation holds real hope for human beings. The electron microscope has shown Dr. Leon Dmochowski and Dr. John A. Sykes of the University of Texas Medical School virus-like particles in leukemia cells of mice, chickens, and men—particles that appear to be strikingly similar. Thus, if a mouse can be inoculated with a virus against leukemia, it may be possible to do the same for man —providing that the human leukemia virus can be found and a vaccine created. To this end, much experimentation on leukemia viruses is being carried on. Other scientists have been experimenting with limited success with vaccines made from cancer patient's own tumors. The common occurrence of cancers in the same family has led to much thought about the part heredity might play as a cause. Biologists have been able, though with difficulty, to breed a cancer-susceptible strain of mice. However, most authorities at the present time agree that there is no real evidence to call heredity a cause of cancer. The fact that several cases occur in a family is regarded as a coincidence due to the increasing frequency of the disease in an aging population. |
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