GENES & CANCER.The environment, not genes, has the biggest impact on who will get cancer, say researchers at the Karolinska Institute in Stockholm and elsewhere. Paul Lichtenstein and colleagues studied 44,788 pairs of twins from Sweden, Denmark, and Finland. They found at least one cancer in 10,803 people among 9,512 pairs of the twins. By comparing the incidence of cancer in identical twins identical twins pl.n. Twins derived from the same fertilized ovum that at an early stage of development becomes separated into independently growing cell aggregations, giving rise to two individuals of the same sex, identical genetic makeup, and (who share all the same genes) to fraternal twins fraternal twins pl.n. Twins that derive from separately fertilized ova and that have different genetic makeup. They may be of the same or opposite sex. (who, like most siblings, share an average of 50 percent of their genes), the researchers estimated what percent of the cancers were hereditary. The risk of being diagnosed with colorectal, breast, or prostate cancer prostate cancer, cancer originating in the prostate gland. Prostate cancer is the leading malignancy in men in the United States and is second only to lung cancer as a cause of cancer death in men. by the age of 75 ranged from 11 to 18 percent for someone whose identical twin already had the disease. For someone whose fraternal twin already had one of the three cancers, the risk was three to nine percent. Using that data, the scientists estimated that genes account for 27 percent of the risk of breast cancer, 35 percent of the risk of colorectal cancer colorectal cancer Malignant tumour of the large intestine (colon) or rectum. Risk factors include age (after age 50), family history of colorectal cancer, chronic inflammatory bowel diseases, benign polyps, physical inactivity, and a diet high in fat. , and 42 percent of the risk of prostate cancer. Genes play an equal or smaller role in leukemia or cancers of the stomach, lung, pancreas, ovary ovary, ductless gland of the female in which the ova (female reproductive cells) are produced. In vertebrate animals the ovary also secretes the sex hormones estrogen and progesterone, which control the development of the sexual organs and the secondary sexual , and bladder, they concluded. That means that the environment--diet, smoking, lifestyle, pollution, etc.--accounts for more than half of the risk of getting most cancers. "The fatalism fa·tal·ism n. 1. The doctrine that all events are predetermined by fate and are therefore unalterable. 2. Acceptance of the belief that all events are predetermined and inevitable. of the general public about the inevitability of genetic effects should be easily dispelled," said Robert Hoover of the National Cancer Institute in an editorial published along with the study. New Eng. J. Med. 343: 78, 135, 2000. |
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