Studies Link Aflatoxin to Liver Cancer
Scientists have identified a specific genetic defect that appears to be responsible for a common form of liver cancer and have determined its probable cause: a naturally occurring carcinogen called aflatoxin B-1 produced by fungi that sometimes grow in certain foods.
Two teams working independently--one on the east coast of China, the other in southern Africa--found exactly the same kind of gene mutation in cells from tumor samples taken from liver-cancer patients in each area.
Both populations, the researchers report in separate articles in today’s issue of the journal Nature, were at high risk of exposure to aflatoxins, as well as to infection by the hepatitis B virus, which is also linked to liver cancer.
Aflatoxins are relatively common in peanuts and corn, although in the United States they are usually at very low levels.
“These findings,” said molecular biologist Mehmet Ozturk of Massachusetts General Hospital’s Cancer Center, a co-author of one of the papers, “are particularly important because the World Health Organization has taken up this problem in the Third World and is conducting studies of the role of hepatitis B virus and aflatoxins as possible carcinogens. Our observations should help those investigators better define their policies and the measures to be taken.”
Although cautioning that the two sets of findings may reflect hereditary conditions or other complications rather than the actions of aflatoxins, Ozturk speculated that both the Chinese and African groups may have suffered a sort of genetic one-two punch. First the hepatitis destroyed sufficient liver tissue so that liver cells were proliferating to repair the damage. Then the aflatoxin-induced mutations took advantage of that condition to grow into tumors.
Various forms of cancer are thought to be caused by defects, or mutations, in genes that regulate cell division. Normally, each gene in a cell’s long helical strands of DNA transcribes an exact copy of itself, which is passed on to the newly created cell.
But sometimes hereditary conditions or chemical influences from the environment derange the copying process, causing slight alterations in the transcribed genes.
These changes may turn some genes--called proto-oncogenes--into accelerators of cell division and may also disable other genes--called tumor suppressor genes--that normally act as brakes on cell division. It is generally accepted that several mutations of the right kind must accumulate in a given cell to turn it cancerous and lead it to multiply into a tumor.
