Could more cancers be caused by inherited faulty genes than we now think?

Professor Douglas Easton, expert on genetics and cancer risk helps us get to the bottom of this question. He first begins by explaining what is in a gene. Faulty genes are changes to DNA, generally speaking. They can only be passed down through families if they are in a persons sex cells. If a genetic change arises during a persons lifetime in other parts of the body, like changes in lung cells due to smoking, then it cannot be passed down through the family.

If there is a fault that raises the risk of cancer being passed down, that does not mean that the person will definitely inherit cancer, it just depends on the kind of fault it is. There are three different types of inherited genetic changes.  There are some genes, such as BRAC1 and BRAC2, which can give a person a higher risk of developing certain cancers, like breast and ovarian cancer.

High risk changes are relatively rare in the general population. A second type of faulty gene is more common and they tend to be very small alterations in the billions of letters that make up DNA. Professor Easton says that not to cause alarm though. He says, its not a matter of whether a person does or doesn’t have such variations- it’s how many they have that matters.  This is because each of the low risk variations just slightly raises the odds that a person will develop cancer. If the person has a lot of these variations, their risk will be higher.

As far as the third kind, Professor Easton says they sit somewhere in the middle.   They raise a person’s risk by more than the common variations, but not as much as the high risk genetic faults. This third type of genetic change is also uncommon.

Scientists think it is unlikely they will find any more high risk genes, like the breast cancer faults. It is the other two types of faults that may prove to be more common than scientists currently think. This is because they are harder to identify in the first place. As technology improves, more variation will be able to be seen.

Professor Easton sums up the answer to the original question nicely: “As we find out more through research, the proportion of cancers that we can explain by inherited genetic changes will likely continue to go up as it already has in recent years. The proportion itself won’t change though; it’s the proportion we understand that may change. But there’s a limit as to how much it can increase by. Lifestyle, and chance, as well as inherited genetic changes, are important in determining who gets cancer”.