Guidance on large bowel surveillance for people with two first degree relatives with colorectal cancer or one first degree relative diagnosed with colorectal cancer under 45 years

These guidelines are intended to consider the place of large bowel screening for relatives of people who have developed colorectal cancer, as there is evidence for an increased risk of colorectal cancer in such people. Colorectal cancer is common and many people have an affected relative. Some 4% to 7% of control cohorts report at least one affected relative, while the greater the number of affected relatives (particularly at younger ages) is paralleled by a proportionately greater personal risk of the disease.(1-4) However, apart from tumour microsatellite instability, which indicates a significant chance of germline mutation in a DNA mismatch repair genes(5 6) and hereditary non-polyposis colorectal cancer (HNPCC),(5) there are no pathognomonic features of familial colorectal cancer that indicate an increased familial risk. Hence, at risk groups outwith HNPCC and FAP have to be defined by empiric risk data from their family history. People with a first degree relative affected by colorectal cancer when aged <45 years or those with two affected first degree relatives have sufficiently high risk to merit consideration for invasive surveillance. This document aims to provide guidance by defining the level of empiric risk at which it is appropriate to consider clinical surveillance. This guidance specifically excludes people whose family history fulfils criteria for HNPCC or other autosomal dominant genetic syndrome associated with colorectal cancer susceptibility. It also excludes people who carry mutations in colorectal cancer susceptibility genes (for example, APC or DNA mismatch repair genes), irrespective of the family history. These scenarios are considered in separate guidance. Although the aggregate risk of colorectal cancer for a group of people can be defined by family history parameters, it is important to consider the heterogeneity of risk for individuals within any risk category group thus defined. Some people who are not offered screening because their family history does not indicate sufficient risk may be destined to develop colorectal cancer. It is essential that this residual risk is made explicit so that it can be appreciated by the person referred as well as by the respective GP.