BY MORTEN BUSCH
For decades, children with Down’s syndrome have been known to have a much greater risk of developing leukaemia than other children. In contrast, new Danish research shows that adults with Down’s syndrome are considerably less likely to develop other types of cancer. This new knowledge may lead to new methods for preventing and treating cancer in general.
Based on registry data from more than 3500 people diagnosed with Down’s syndrome, the study compared their number of cases of cancer with those for the general population. Although, as expected, children and adolescents with Down’s syndrome had 5–6 times as many cancer cases, the number of adults with Down’s syndrome who had cancer was half the national average.
The researchers highlighted various factors, including health-related behaviour, that may explain the reduced prevalence of cancer among adults with Down’s syndrome. For example, the percentage of adults with Down’s syndrome who had lung cancer was only 10% of that among the general population. This may be because fewer people with Down’s syndrome smoke. Researchers also suggested less sun exposure and less sexual activity as possible explanations, since sexually transmitted human papillomavirus is the most common cause of cervical cancer.
Nevertheless, there are probably genetic causes for this reduced risk of cancer among the adults. It is caused by an abnormality on chromosome 21. This means that a person with Down’s syndrome has 47 chromosomes instead of 46 – often with an extra copy of chromosome 21. This chromosome contains more than 200 genes, many of which are believed to be associated with cancer: for example, genes that code for endostatins, protein fragments that are known to counteract cancer.
The reduced prevalence of cancer among the adults applied to all types of cancer that involve solid tumours, except for testicular cancer. It is therefore worth examining more closely which factors might halve the risk of cancer, since this will help to better understand cancer in the general population and might thereby reduce cancer generally. Further, the considerable age differences in cancer among people with Down’s syndrome should lead to different screening strategies. The reduced prevalence of cancer among the adults offsets the much higher prevalence among the children and adolescents, so the overall average prevalence is the same as that of the general population.
“Low risk of solid tumors in persons with Down syndrome” has been published in Genetics Medicine. In 2013, the Novo Nordisk Foundation awarded a grant to lead author Henrik Hasle, professor and chief physician at Aarhus University Hospital, for the project Pharmacogenetics of Childhood AML: Individual SNP Risk Profiling for Minimizing Future Treatment-related Toxicities.