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Familial colorectal cancer risk: only part of the truth is in the genes
For decades, health experts have been pointing out that people who have had colon cancer in their family have an increased risk of developing the disease. But when it comes to this familial risk of colon cancer, the role of genes has long been overestimated. This is the conclusion reached by researchers from Germany.
“Colon cancer is known to have a family history: in large observational studies, researchers have shown that first-degree relatives (parents, siblings, children) of colon cancer patients themselves develop colon cancer more often than other people - their risk is about two to three times greater increased, ”explains the cancer information service of the German Cancer Research Center (DKFZ). But when it comes to the family's increased risk of colon cancer, the role of genes was overestimated. This is the conclusion reached by DKFZ scientists in a recent study.
35 percent hereditary
As the DKFZ wrote in a message, colorectal cancer is the third most common cancer worldwide. It is currently assumed that 35 percent of the disease is hereditary. A family history is one of the most important risk factors. In addition, researchers have identified around 100 tiny gene variations that are widespread in the population (single nucleotide polymorphisms, single nucleodid polymorphisms, SNPs) and that affect the risk of colon cancer.
Current results of the DKFZ scientists headed by Hermann Brenner and Korbinian Weigl, however, now suggest that these SNPs explain a significantly lower proportion of the familial increased risk of colorectal cancer than previously assumed. The researchers first checked the common statistical methods that are used to estimate this percentage. According to the information, they noticed a number of weaknesses in the calculation, which overall lead to a significant overestimation.
"In particular, the current methods used assumed that the family cluster is ultimately one hundred percent genetic," says Korbinian Weigl, first author of the study, which was published in the "International Journal of Cancer". “Based on this, they then calculated what proportion of this can be explained by the gene variants known to date.”
Risk factors such as family eating habits are probably more serious than expected
The team around Brenner and Weigl evaluated the data from a total of 7,927 subjects in a case-control study - including 4,447 patients with colorectal cancer and 3,480 healthy people who served as a control group. "We have developed a new calculation method that does not start from the basic assumption that the family risk is entirely caused by genetics," explains study leader Hermann Brenner. Using this method, the researchers then evaluated the data of their subjects.
In fact, the influence of SNPs using this method was significantly less than expected. While previous calculations gave the previously known gene variants a share of 9.6 to 23.1 percent of the increased familial risk of colon cancer, the new calculations by the DKFZ scientists result in an estimated influence of the SNPs of between 5.4 and 14.3 percent .
"The results fit very well with the results of another DKFZ study that was published last year," says Brenner. It had been shown that the half-sibling of colon cancer patients increased the risk of developing the disease themselves as well as that of “real” siblings. "This suggests that common risk factors, such as special dietary habits, smoking or a lack of exercise play a significantly larger role than previously thought."
Use options for colorectal cancer screening
For the future assessment of the individual colorectal cancer risk, however, this in no way means that the gene variants that are associated with an increased risk have become meaningless. "Rather, our study shows how important it is to consider both genetic and other risk factors in the family equally in order to arrive at a realistic assessment," says Weigl.
Or to put it another way: If you only have a few conspicuous gene variants in your genome, you must not weigh yourself in safety if, for example, your lifestyle increases the risk of colon cancer. Conversely, despite unfavorable genetics, colorectal cancer does not have to be fate if individual behavior lowers the risk. In any case, it is advisable to use the very effective options for colorectal cancer screening. (ad)
Author and source information
This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.
- German Cancer Research Center: familial colorectal cancer risk: only part of the truth is in the genes, (accessed: 29.09.2019), German Cancer Research Center
- International Journal of Cancer: Establishing a valid approach for estimating familial risk of cancer explained by common genetic variants, (Access: 29.09.2019), International Journal of Cancer
- Cancer information service: colorectal cancer: risk factors and prevention, (access: 29.09.2019), cancer information service