issue 198 - August 1989
What causes cancer? That depends on who you ask.
Differing views are based as much on political opinion and economic
interests as on scientific research. Howard Frumkin outlines the
controversy and the stakes involved for both North and South.
Cancer is more than a disease; it's also a powerful symbol - due in part to the way it claims its victims. But how you describe the symbol is a matter of political preference. For example, a conservative worried about left-wing subversives might see cancer as a process that begins insidiously in small cells, infiltrates silently and relentlessly, destroys the infrastructure as it goes. and eventually brings down the entire system. On the other hand, a social activist upset by power-hungry corporations might see cancer as a process distinguished by a voracious appetite for resources: a disease that invades and colonizes parts near and far, subverts local production. and eventually establishes a dominion.
No matter what your view there are some facts about cancer that are uncontested. We do know that cancer is a collection of diseases that share a common characteristic - uncontrolled growth in one of the body's tissues. Almost any tissue in the body can be a site for cancer. In developed nations, the most common types are in the large intestines, the female breast, the prostate gland and the lungs. In the Third World, the stomach, liver, and uterine cervix are more common cancer sites.
As tumors grow, they may compress or erode adjacent parts of the body. Alternatively, they may send offshoots ('metastases') to distant parts of the body, which can themselves cause symptoms. Cancer can also increase the risk of infection and create chemical imbalances in the body.
It is now accepted that environmental factors play a major role in cancer - 'environmental' here is used broadly to include toxic chemicals, cigarettes, diet, sexual habits and radiation. One basis for this is geographic comparisons. In northern Iran, there are 170 cases per year of cancer of the esophagus for every 100,000 women. That compares to about two per 100,000 worldwide and about 0.4 in Utah in the United States. Stomach cancer strikes 90 of every 100,000 Japanese men annually; yet in Cali, Colombia it affects 45 men per 100,000 and in Ibadan, Nigeria, only seven per 100,000. Many cancers exhibit this variability.
Studies of immigrants also suggest an environmental influence on cancer. Among Japanese migrants to the United States, it took only two generations for their steep stomach cancer rate to decrease to prevailing US levels.
Lively controversy has raged over many aspects of cancer. The 'establishment' position, backed by industry, is that industrial products have little to do with cancer. Instead, 'lifestyle' factors like cigarettes, alcohol and diet are emphasized. The 'radical' view, supported by environment and labor activists, places more emphasis on industrial exposures, both at work and elsewhere.
This controversy centres around several questions. Is cancer really on the rise or not? What causes it? What role do chemicals, radiation and other 'carcinogens' play? How critical is tobacco? How should carcinogen exposure be regulated? What are the correct priorities for cancer research?
Some writers argue that industrial nations are in the midst of a cancer epidemic, a twentieth-century version of the plague. It's true that absolute cancer rates have increased in recent years, partly due to aging populations (cancer is primarily a disease of older people), elimination of competing causes of death, and better diagnosis. However, even when these factors are removed there are still increases in cancer over time. But the increases are limited to certain kinds of cancer, among certain age groups, and in certain locations. In the US, lung, breast, prostate and bladder cancer are increasing; stomach and uterine cancer are declining; and leukemia and pancreatic cancer are stable. So, while some cancers are on the rise, the cancer 'epidemic' really comes down to lung cancer.
What causes cancer? We know that a healthy cell becomes malignant following changes to the genetic molecule, DNA. Recent evidence suggests that we carry specific genes, called 'oncogenes', that are especially prone to mutations resulting in cancer. Some peopIe may inherit a tendency to develop certain cancers. But even in those cases something has to happen to transform normal DNA into malignant cancerous DNA. Some of the triggers are well known: viruses, radiation and some chemicals may damage DNA in a way that results in cancer. But with individuals, it is often impossible to specify just what 'caused' a cancer. To make matters worse, there is no one-to-one correspondence between carcinogens and cancer. There is no exposure that inevitably results in cancer (much as it may increase the probability); and there is no cancer that is invariably associated with a particular exposure. The best we can say at the moment is that all 'causes' of cancer are only probable.
This uncertainty has meant that it has been very difficult to rank and quantify the importance of diet, tobacco and workplace chemicals. In 1978, a US report attributed 20-40 per cent of the nation's cancer to workplace causes. Three years later, UK epidemiologists Sir Richard Doll and Richard Peto estimated that only four per cent of cancer is workplace-related. The higher figures are acknowledged to be exaggerated: most estimates converge in the five to ten per cent range. But even that is a great deal of cancer - 20,000 to 40,000 preventable deaths in the US each year.
Tobacco is by far the major cause of cancer in the West. Yet the tobacco industry has consistently denied that tobacco causes disease. Combining pseudo-scientific arguments with aggressive marketing pitched at young people and the Third World, it has set the standard for cynical, mendacious corporate conduct.
Social activists are also wary of targeting 'lifestyle' factors like cigarettes since these have been used to divert attention from toxic substances. Perhaps that's why critics of the cancer establishment have paid scant attention to tobacco-related cancer. It brings to mind a trade union meeting where members rage against a relatively minor carcinogenic exposure while filling the meeting room with cigarette smoke. We must acknowledge tobacco's monstrous role and fight to minimize it.
The regulation of carcinogens is also controversial. One reason is obvious: industries resist change because they want to avoid the costs of cleaning up. In addition, we do not know whether there is a 'threshold' level of carcinogen exposure that is safe. Theoretically, a single molecule could transform a normal cell into a cancerous one, which would seem to call for an absolute ban on carcinogen exposure. On the other hand, it may be that small exposures are harmless and perhaps even essential, and that up to a point our bodies can detoxify most chemicals, including carcinogens.
This creates a quandary. Ideally, regulations would specify a proven safe level of exposure and ban exposures above that level. But it's virtually impossible to specify such a level, or prove that it even exists. Public health advocates argue for a conservative approach that tolerates no carcinogenic exposures. Corporations claim that specified levels of exposure should be permissible. They demand that regulators justify such levels with a cost-benefit analysis that weighs the cost of compliance against the number of lives to be saved. Even though the necessary data for this approach is hardly ever available, a 1980 US Supreme Court decision on benzene standards approves this kind of analysis. This will be hotly-contested terrain for some time to come.
How should cancer research be targeted? A huge research establishment has focused on treatment rather than prevention. But after decades of effort most cancers are treated no more successfully today than in the past. Some of the most obvious strategies for fighting cancer - primary prevention .and early detection - have been ignored and deserve a great deal more emphasis.
In the Third World, cancer is not as important as many other diseases. While it accounts for 22 per cent of deaths in the US, in Peru it accounts for only eight per cent and in Guatemala less than four per cent. Who gets cancer - and why - also differs substantially from the West, as do prevention strategies.
The distribution of cancer in developing countries is determined by three main factors. One of the most important is infectious agents like viruses. For example, where liver cancer is common, the hepatitis B virus is also widespread. In regions where cancer of the nose and throat is high, the Epstein Barr virus appears to be to blame.
Another factor is the rapid spread in the Third World of chemicals, drugs, pesticides and consumer products that may be carcinogenic but whose sale and use is not subject to controls. The third factor is the ferocious campaign of the tobacco companies to expand their sales in the poorer countries.
The infectious causes of cancer can be reduced through vaccination campaigns and research. Regulating industrial pollution and restricting dangerous pharmaceuticals could also reduce risks. But the key question is how to balance public health regulations with national development priorities in the developing world.
Progress in tackling cancer requires more than technical advances in medical treatment. It demands better information about causes as well as a commitment to safe levels of exposure. In the end that means finding alternatives to carcinogenic chemicals. But above all it means learning to balance risks and benefits in more humane ways - making sure that cancer is not another price to be paid for being poor and powerless.
Howard Frumkin is a cancer researcher at the University of Pennsylvania in Philadelphia.