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What Causes Cancer?

Microscopic View of Lung CarcinomaAfter examining data on 44,788 pairs of twins, researchers report that, in most cases, environmental factors have the greatest effect on cancer risk. As reported in the New England Journal of Medicine, researchers studied twins listed in Swedish, Danish, and Finnish registries, concluding that inherited genetic factors make a minimal contribution to cancer risk.

Heredity was judged to play no detectable role in cervical or uterine cancer. For lung cancer, genetics accounted for 26 percent of risk. The remainder is due to environmental factors, such as smoking and other dangerous exposures. For cancers of the breast, ovary, and prostate, the environmental component was estimated at 73, 78, and 58 percent, respectively.

Lichtenstein P, Holm NV, Verkasalo PK, et al. Environmental and heritable factors in the causation of cancer. N Engl J Med 2000;343:78-85.

Does 'Five-Year Survival' Equal Progress?

In the war against cancer, "five-year survival" is used as a primary measurement of progress: the more cancer patients who live at least five years after diagnosis, the farther we have come in the fight. A new study in the Journal of the American Medical Association (JAMA) suggests that this calculation may be misleading.

Researchers examined data on 20 types of cancer between 1950 and 1995, looking at incidence, five-year survival rates, and mortality. Although five-year survival rates increased for all 20 cancers, occurrence decreased in just 5. While death rates from 12 types of cancer declined, they increased for the remaining 8.

The U. S. Department of Health and Human Services interprets increases in five-year survival as proof of success, saying that "much of the research into early cancer detection and treatment paid off." However, JAMA researchers point out that patients today are more likely to be diagnosed when cancer is at a microscopic level, making five-year survival more probable simply due to early detection. When assessing progress in the battle to end cancer, the study authors argue for using population-based mortality rates. As it stands, five-year survival shows surprisingly little relationship to overall mortality rates.

Welch HG, Schwartz LM, Woloshin S. Are increasing 5-year survival rates evidence of success against cancer? JAMA 2000;283:2975-8.

Toxic Fish Compound Ends Up in Breast Milk

Researchers in Japan have found high concentrations of the chemical polybrominated diphenyl ethers (PBDE), which is used as a flame retardant, in mother's milk and marine life. PBDE generates a substance similar to dioxin, a known carcinogen and endocrine disrupter.

The study showed that fish and shellfish living closest to the shore carried the highest concentrations of PBDE. Not surprisingly, researchers also found higher concentrations in the milk of women who consume a large amount of fish. There is no regulation on PBDEs, and Japanese manufacturers continue to produce 50,000 tons of it each year.

The Japanese Times. June 21, 2000.

Vegan Diet May Cut Risk of Prostate Cancer

British researchers report more evidence that a diet free of meat and dairy products may lower a man's risk for developing prostate cancer. The Oxford study of 696 men found that IGF-I levels were 9 percent lower in vegan men than in meat-eating men. IGF-I, insulin-like growth factor, is believed to play a key role in causing prostate cancer.

The study also mentions previous population studies showing that countries with low consumption of animal products had lower rates of the disease. The American Cancer Society predicts that there will be about 180,400 new cases of cancer in the U.S. by the end of 2000. Approximately 31,900 men will die of the disease.

Allen NE, Appleby PN, Davey GK, Key TJ. Hormones and diet: low insulin-like growth factor-I but normal bioavailable androgens in vegan men. Br J Cancer 2000;83:95-7.

Cancer-Fighting Ingredients in Apples and Carrots

Two new studies confirm the cancer-fighting power of plant foods. Scientists at Cornell University performed laboratory tests on human colon cancer cells and found that apple skin inhibited the growth of cancer cells by 43 percent. Tests on liver cancer cells were even more effective. Researchers believe it is the combination of phytochemicals in plant foods that reduces cancer.

It's no surprise that the second study also found carrots to be high in antioxidants, compounds that prevent free radicals from damaging cells and causing diseases such as cancer. However, scientists found that cooking and pureeing carrots increases their antioxidant level more than three times. Researchers report that heating and softening the carrot's tissue allows cancer-fighting phenolic compounds attached to the cell wall to be released. And, keeping the outer skin on carrots, as with other vegetables and fruits, retains numerous extra cancer-fighting compounds.

Eberhardt MV, Lee CY, Liu RH. Antioxidant activity of fresh apples. Nature 2000 22;405:903-4.

Cancer Risk from Animal Organs

Cancer Risk from Animal OrgansA new study has found that cancer-causing viruses can be spread between various species in the wild and can easily jump to humans. The discovery intensifies recent findings revealing that hearts and kidneys taken from pigs contain potentially deadly viruses. As a result, British health authorities have imposed a moratorium on all xenotransplant (cross-species transplant) surgeries, although biotechnology companies continue research in this area.

The study authors note that just because animals were found to have certain viruses doesn't mean they will necessarily show signs of illness. However, when viruses jump species they often acquire pathogenic properties, as was the case with HIV. What's more, such illnesses can take decades to show effect. Opponents of xenotransplantation hope that a combination of prevention programs and better access to available human organs will eliminate the push for animal hearts, livers, or any other organs.

Natural Environment Research Council.


Winter 2001 (Volume X, Number 1)
Winter 2001
Volume X
Number 1

Good Medicine

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