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CANCER - A LONG TERM BIOCHEMICAL PROCESS
Cancer appears to strike unexpectedly and without any warning. Even if it is not fatal it can seriously diminish the enjoyment life. Yet it is produced by a biochemical process that probably is proceeding in everyone. And the result of this process should be potentially predictable long in advance. It is useful to understand better the macro BioChemical process that produces cancer. This understanding plus an identified needed change in habits should help us avoid experiencing this dismal problem.
Specific chemicals known as carcinogens probably cause most of the cancer now experienced by humans. A great deal is known about them. What is not generally realized is that with carcinogens and a controlled experiment we can produce cancer in populations of animals in a highly predictable way. And cancer probably is produced similarly in populations of people at a potentially predictable way.
One standard test for a carcinogen is to paint measured amounts of the chemical on the backs of members of a group of 25 or 50 mice. This painting is done at various time intervals, but usually 3 times per week. (Other tests feed carcinogens to the animals) For a fairly potent carcinogen, nothing will happen during a first 140 days. Then at 150 days a tumor will appear on the painted site on one mouse. Others then will start to get these tumors, and by 210 days half of the mice will have them. By 300 days all the mice will have them. And at 210 days first tumors will have developed to carcinomas or cancer. At 290 days half of the mice will have cancers and some will have died of them. By 420 days all mice will have had cancer and will be dead of the disease.
Figure “Carcinogens1” shows the tumor results of such experiments on mice painted with various concentrations of a potent carcinogen. The percentage of mice with tumors is plotted vs. the. days of exposure using a probability scale for the percentage and a logarithmic scale for the exposure time. (A variation of this method is termed probit by statisticians). Note the striking effect of concentration of the carcinogen. For the 0.30% concentration half the mice had tumors in only 80 days. It took over 400 days for this same result on the 0.01% concentration. Although not shown here, cancer developed at a time averaging 40% higher than that needed for tumors. The important message from this graph is that the results were highly predictable. Repeating this on similar colonies of mice produces the same result. The time needed for half of the mice to develop tumors provides a measure of carcinogen potency, and this potency has been measured for all kinds of chemicals.
Figure “Carcinogens1”
Much more about how cancer develops is learned from these experiments. Less frequent painting produces less cancer. Washing the painted area each day significantly reduces but does not halt the cancer produced. Combinations of carcinogens can be particularly effective. Using this experiment on other animals usually produces similar results, but over differing time. And what happens to mice in 300 days vs their usual day 500 day life expectancy appears to happen to humans at ages 50 vs. their life expectancy of 75-80. This suggests cancer proceeds in relationship to the life of the involved body cells.
A most important message from these experiments is that there is an induction time needed for first incidence of tumors and cancer. With 0.30 MC half of the mice had tumors in 80 days. But it took more than 50 days or one tenth of their life expectancy for the first 1% to be affected. For the mildest carcinogen the plots suggest that about 300 days or much of their life expectancy of 500 days for even a first 1% to be affected. The key factor that produced cancer was duration of exposure. Also animals show differing resistance and need differing exposure times to obtain cancer. Rats as example are resistant to cancer from carcinogens.
Unfortunately, humans are NOT adequately resistant. Figure “Carcinogens2” shows how lung cancer develops similarly on humans from exposure to carcinogens using the same type of plots used for the mice experiments. A difference is that for the humans the results are shown in terms of actual deaths from lung cancer. And the time is changed from days of exposure to carcinogens to years of exposure. Many men and women have been faithfully painting their lungs with carcinogens from cigarette tar for decades, thus providing the same kind of experimental data as those obtained on the mice.
Figure “Carcinogens2”
Cigarette tar is a rather weak carcinogen that tests on mice similar to 0.01% methylcolanthrene. This explains in part why only 5-12% of men who smoke are dead of lung cancer after many years of smoking. But cigarettes also cause many more deaths from coronary disease and other causes. Most carcinogens in food and pollutants also are of modest potency. But results from some other carcinogens included in above plot show that they are far more potent than cigarette tar in producing cancer.
The slopes of the plots in these figures identify in part the genetic variability of the individuals in the populations. The flat slopes for the mice are in part because they were carefully in breed to achieve this, and because of the precision of the experiments. The much higher slopes for humans are due to their much greater differences in genetic susceptibility and their differences in other habits. But the key observation here again is that cancer is produced by duration of exposure. It took may years of smoking to elicit first statistically measurable events of lung cancer in men. From this time on duration of exposure increased risk of lung cancer risk exponentially. A message here is that an attempt to measure a risk of cancer from a shorter than needed time of exposure to an agent will fail. Note in the above that at takes 20 years before men start to die from their cigarette smoking. A sophisticated clinical study of cigarette smoking done for an extensive 10 or15 years of duration probably would be unable to 'Find' any effect of smoking on cancer within its limits of error.
These hardly are new observations. These charts were prepared by this author more than four decades ago when involved in an important project on industrial cancer. Yet part of an entire new generation of statistically oriented health researchers today appears unaware that exposure time is a major factor in the development of cancer. Study after study cites risk ratios for cancer with no included information on duration of the involved factors. Others propose clinical studies to measure how cancer develops from agents that could not possibly produce any cancer within the time planned. This lack of research data on duration provided a key problem in developing Life Ahead factors for cancer, and this is discussed extensively in the Health Research Library.
Think now about how cancer can be expected to develop in the human body. Carcinogens from air pollutants including those from smoking go into the lungs where they become trapped and deposit on tissues. There probably is little washing action to remove them from lungs and thus the lung surface involved builds up steadily with time. Some pollutant chemicals also may get down into the digestive organs and into the blood stream and this will be enhanced if a person smokes and eats at the same time. Carcinogens in foods – and these may number in the many dozens - go into the mouth, throat, and into the stomach and digestive organs. Here they remain in contact with body tissues for some time period and initiate the cancer process there. Nearly any kind of a tar will include some chemical agents that have carcinogenic properties. Frying food or cooking over a fire almost certainly will produce some added carcinogens that will be passed down through the body. Most tars as carcinogens are not soluble in an aqueous environment and can pass through the body. Alcohol is a mutual solvent that can bring about closer (and more harmful) contact of carcinogens with body tissue. Thus alcohol plus smoking is a particularly harmful combination. This does not explain how cancer of the breast or some female organs can become involved. Thus the cancer promoters also appear to be transferred via the blood. Little may happen for 10 or even 20 years of this process. But then suddenly the tumors and cancer will start to develop.
The key problem is “What can we do about it.” Life Ahead brings together those factors that research verifies should help, and identifies them and their possible contribution toward reducing risk. Risk of cancer cannot be reduced by lifestyle as much as can cardiovascular diseases. But the program still suggests that cancer risk usually can be reduced by three or more fold by modification of diet, exercise, and other habits. But these habits must be modified for many years - and desirably for a full lifetime - for real benefit.
Medical focus today is on finding precursors of cancer such as tiny tumors and eliminating these before they can develop aggressively. Mammography often does this successfully for breast cancer. Yet if cancer development takes a usual 20 years in humans to become visible even at a minimal tumor level, it must also have been proceeding and leaving some evidence trail throughout those initial 20 years. Today’s real need is to find a way to find out where this ‘pre-tumor’ cancer is developing. Again this hardly can be a new idea. But it should be a very serious part of research on ways to stop cancer. Recall that duration of exposure was a key factor determining extent of the atherosclerosis that is a key cause heart disease. Duration of exposure also is a key factor in the development of cancer. A new contribution of Life Ahead is that it tracks duration of exposure and the increase in risk caused by this for each succeeding year of life for important factors that produce the major life limiting diseases. This vitally important factor usually is overlooked in risk factors and in other models of health.
