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| |  Sibling Of Twin With Breast Or Testicular Cancers At High Risk Too LONDON, ENGLAND -- December 12, 1997 -- Breast and testicular cancers may be related to pre-natal factors that affect the fetus. High levels of estrogen (a risk factor for breast and testicular cancer) may be present in the womb in twinning, especially for non-identical (dizygotic) twins. Professor A.J. Swerdlow, Epidemiological Monitoring Unit at the London School of Hygiene and Tropical Medicine, and colleagues from London report findings in this week's The Lancet that the twin of an individual who has breast or testicular cancer (probands) is at high-risk of developing these cancers. The investigators gathered information on breast and testicular cancers entered on to the national cancer-registration records during 1971-89. From these records, they identified all twins with these cancers by crossmatching the records with the birth register, which indicates twins. The family physicians of all these probands were contacted and, with their permission, the probands were sent questionnaires that asked about whether they were identical or non-identical twins. For those who agreed, the investigators also sent questionnaires to their twin. Of the 694 probands identified, 500 had breast cancer, 194 had testicular cancer. The risk of developing breast cancer was non-significantly higher among dizygotic twins of probands than among monozygotic twins aged younger than 30 years, but not at older ages. For testicular cancer, the overall risk was highest in dizygotic twins compared with monozygotic twins. For the monozygotic twins of probands who developed breast cancer before the age of 35 years, the risk was 34.7 times higher than in dizygotic twins, and for testicular cancer, the risk was raised 37.5 times in monozygotic twins compared with dizygotic twins. Therefore, young monozygotic twins represent an extremely high-risk group that is identifiable without genetic testing and costly screening. The investigators point out for breast cancer that "To inform the women of their high risk if they were not aware of it would not be ethical, so the decision on appropriate action can, perhaps, only be made clinically on an individual basis," the researchers write. For testicular cancers, the investigators conclude that, although there seem to have been no previous studies of this cancer, the risk they found in monozygotic twins of probands is likely to indicate correctly that there is a greatly raised risk in such men "We estimate a cumulative risk by the age of 40 years of 14 percent," they write, adding counselling should be considered for these twins.
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