• Question: To what extent is cancer linked to your genes? @swbgs

    Asked by Borlasian to Barbara, Matt, Ravinder, Sophie, Tristan on 7 Mar 2015.
    • Photo: Matthew Moore

      Matthew Moore answered on 7 Mar 2015:

      Great question!

      First of all, cancer isn’t just a single disease, there are 100 types of cancer. How much genes affect these various cancers varies greatly!

      All cancer is genetic in that it stems from an abnormality in your DNA, but this is as a result of mutations in the cells. This is how sunbeds, smoking, chemical exposure etc can cause cancers, by damaging the DNA.

      There are examples however of versions of genes which, when inherited (when you’re born with them) make you really likely to get cancer. An example of this is the BRCA1 and 2 mutations, which when inherited increase the chances of getting breast cancer –this can be as much as an 85% chance of getting breast cancer because of this mutation.

      The BRCA mutations were first discovered after a study observed that there was a history of breast cancer in certain families, in the 90’s. Now tests are available to find out if somebody is carrying a BRCA mutation.

      So usually it varies, it’s complicated and unclear why some people appear to be more likely to get cancer and difficult to tease apart from complex environmental factors, but there are also examples of genes such as BRCA where the probability of a carrier getting a particular cancer can be calculated.

    • Photo: Barbara Shih

      Barbara Shih answered on 7 Mar 2015:

      This is an interesting questions. Short answer is “we don’t know – probably depends on the cancer”. Matt has already mentioned most of the points I was going to say. Adding a bit of debate to your question, a group of researchers have proposed environmental factors (e.g. smoking) and inherit genes only accounts for 1/3 of the chances for cancer. Their study suggests that the life-time risk of different types of cancers is highly related to how many times the stem cells of that tissue divide – more divisions means more chances for mistakes. For example, skin basal cells divide a lot more times than bone cells, and basal cell carcinoma (skin cancer) is much more common than osteosarcoma (bone cancer). They’re saying a large part of getting cancer is simply “bad luck”. (http://www.sciencemag.org/content/347/6217/78)

      For certain disorders, cancer is very much related to genetics. People who have Xeroderma pigmentosum (genetic disorder caused by mutations in genes involved in repairing damaged DNA) have a much higher risk of developing skin cancers – without sun protection, half of the children with this condition would get skin cancer by the age of 10.

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