Tuesday, April 29, 2008

Cancer and animals

Cancer experiment on monkey

Cancer relates to questions of animal ethics in two major ways:

1) Animal experimentation

2) Human nutrition and lifestyle.

Let’s start with animal experimentation. This broad field branches out into two main areas in association with cancer:

a) animal testing of carcinogenicity (cancer-inducing quality) of substances

b) cancer research on animals to find cures for humans.

Animal testing of carcinogenicity

Carcinogenicity studies on animals are used for all kinds of compounds, in particular synthetic substances, pesticides, food additives and all sorts of other chemicals. They, especially pesticides tests, have been largely instigated by the environmentalist movement, which has created, since Rachel Carson’s book Silent Spring onwards, a public hysteria about a phantasmic connection between human cancer and man-made chemical substances in the environment.

The crude reality is that animal tests are a totally inadequate means of finding out whether a substance causes cancer in human subjects not just because of the important obstacle represented by species difference but also, more specifically, because of the extremely high dosages to which lab animals are subjected over a short period of time, as opposed to the low levels (mostly residues) to which humans are exposed over a long time.

Half of all the substances administered to animals at these near-toxic levels are carcinogenic in the test subjects, purely because of the local damage they cause in virtue of their massive amounts. Many of these chemicals are well-known for not causing cancer in humans at all.

What increases the risk of cancer in humans is something completely different, and we’ll get to that when we later discuss nutrition and lifestyle.

Of all the substances in our environment, one of the most seriously and lethally carcinogenic is asbestos, and here animal experiments have continuously misled researchers into believing that asbestos was safe simply because lab animals subjected to it did not develop the deadly form of cancer that we have known for decades to plague asbestos workers: mesothelioma. So, thanks to animal research, legislative measures to ban asbestos were delayed in the West by several decades, while workers and their families kept getting ill with asbestosis and tumors which could not be replicated in animals and therefore, so researchers thought, animal experiments had not “validated” the asbestos-mesothelioma causal connection.

Cancer research on animals

Cancer research on animals consists in taking healthy animals, mostly rodents, and trying to make them ill with cancer by various artificial means, sometimes successfully and sometimes not, in order to test on them possible treatments designed for humans. When researchers “luckily” succeed in making a healthy animal develop cancer, the tumor is not the same as the human one that it is supposed to model.

First of all, the aetiology of the disease is completely different. The causal mechanisms that induce cancer in humans are practically impossible to reproduce in a lab using animals. The most frequent causes of human cancer by far, as we shall see in more detail when we examine lifestyle, are smoking habits, bad nutrition choices, alcohol-drinking, lack of exercise, and all of these causal factors accumulate over a long period of time, often a lifetime, gradually and slowly. Lab animals, on the other hand, have to be made sick quickly, and they do not naturally indulge in all those cancer-risky lifestyle habits of which so many humans are so fond. So the means to induce cancer in them are necessarily artificial, different from the human causes, and designed to produce a rapid response.

Some common human cancers, like prostate, rectal and colon cancers, are rare in rats and mice, the cancer researchers’ favourite (most used) species. So experimenters have to labour particularly hard to inflict these tumours on rodents.

Regardless of the causes, moreover, cancer is not the same disease in different species of animals, human included. Cancer is not, strictly speaking, a disease, but an umbrella encompassing several ailments, according to the distribution of the various cancer sites. But animal tumours are not the same entities as human ones, even when they affect the same sites or are given, for reasons of convenience, the same name.

For instance, human bowel cancer affects a different part of the intestines (the colon or large bowel) from rats’ bowel cancer (the small bowel). And the mechanism of colon cancer in the two species is dissimilar: humans die because the cancer metastasizes, namely spreads to other parts of the body, whereas rats die because the colon is obstructed.

So, basically cancer researchers are studying something completely different when they use animals. The latter are not models of human cancer at all.

As a consequence, it should come as no surprise to learn that many of the various cancer treatments making the headlines, which have been tested on animals and found to be effective in them, turn out to be, when later administered to human subjects, ineffective or even harmful.

Human nutrition and lifestyle

We do not yet know how to cure cancer. Despite some improvement in therapy, this often fatal disease remains elusive to understand and refractory to cure. However, we know an awful lot about the risk factors that increase the probability of contracting cancer. Of all the areas of cancer research, the greatest progress has been made in cancer prevention. To stop cancer from developing in the first place remains the best option that we have.

And this, from many viewpoints (except perhaps if you consider laziness, addiction and force of habit), is extremely good news. Because all the major causes, or risk factors, of cancer are entirely under an individual’s control. They all pertain to a person’s lifestyle.

First comes tobacco, by far the major contributing factor to cancer incidence rates.

Then comes diet. We know very well what a cancer-preventing nutrition (and preventing other major diseases too) should be. Medical authorities and health experts advice is simple: avoid completely certain kinds of meat (namely, cured or processed meats like bacon and sausages), eat as little red meat as possible, reduce all types of meat and animal fats, replace them with proteins and fats of vegetable origin, and eat more fresh fruits, vegetables and grains.

And here we come to the other connection between cancer and animal ethics.

It looks like both our health and our morals point in the same direction. There is no real conflict of interests: what is good for us is also good for other animals, who could be spared the life-long torture of imprisonment in factory farms and the short but agonizing experience of the slaughterhouse.

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