Uses of genetic testing for cancer prevention

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Abstract Predicting the risks for any individual of developing future disease introduces the possibility of mitigating the cancer risk by one or more intervention. Intervention may be a modification to lifestyle, early or more frequent cancer surveillance or potentially life changing major surgery. Risk assessment utilising genetic testing may be delivered at the individual or the population level. Traditionally, testing for high risk genes was delivered through typically genetic services well experienced at rare disease genetics. Predictive testing predicts high risks for cancer in healthy individuals in the context of a strong family history. With the advent of targeted cancer treatments there has been a move of the initial genetic test into mainstream oncology. With new approaches increasing the efficiency and reducing the cost of sequencing, many laboratories sequence large panels of cancer susceptibility genes, few are high penetrance and in the largest panels, many have only very weak evidence of risk association. Laboratory interpretation of sequence variants is largely manual so the more sequence is interrogated, the more variants from the expected sequence - each of which has to be interpreted. This is now the time and cost limitation. Finally even high risk genes are never 100% penetrant, penetrance is modified by hundreds of single nucleotide polymorphisms (SNPs) identified through genome wide association studies (GWAS). Communicating the purpose of a genetic test and the potential outcomes and consequences for the patient and for other family members is particularly challenging during cancer treatment. Oncologists who take on this responsibility need a clear understanding of the nature and variability of genetic risk and the clinical utility of any gene tested. Additional training in this area is recommended for oncologists who wish to ensure their patients have the best advice and care.