Using genetics to understand cancer risk is not a new idea. Take, for example, breast cancer, the most common cancer amongst Western women. We’ve known since the 1990s that mutations in the BRCA genes influence a woman’s chances of getting breast or ovarian cancer. Whilst this has led to a range of important screening initiatives that have saved lives, women with mutations in these genes only account for a small proportion of all breast cancer cases. It’s also the case that not all people with a BRCA mutation go on to develop breast cancer.
What’s more, tests for BRCA mutations are only really prescribed (and reimbursed by medical insurers) for the small subset of the population where prior information, such as a family history of early onset breast or ovarian cancer, points towards these gene variants having a putative role in the disease. (Angelina Jolie, who famously had a mastectomy following a positive test for a BRCA mutation, knew beforehand that her mother had died from ovarian cancer caused by a BRCA mutation.) Many others with BRCA mutations but who don’t have a family history of disease will not have the opportunity to be tested. So, whilst BRCA genes has been transformative for defining risk in families, as a general assay for disease risk, such tests have limited broad-scale utility.