Oral Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2018

A gastroenterologist’s perspective of the implications of risk stratified colorectal cancer screening (including that based on genomic assessment) (#36)

Hooi C Ee 1
  1. Sir Charles Gairdner Hospital, NEDLANDS, WA, Australia

Colorectal cancer (CRC) is an excellent disease for screening given the long latency between precancerous adenomatous polyps and invasive malignancy. Screening strategies leading to colonoscopy are effective in detecting cancers at earlier stages, as well as preventing cancer development by polyp removal.

Increasing age is a major risk factor for CRC and in Australia the National Bowel Cancer Screening Program invites participants on the basis of being aged between 50 and 74 years inclusive. Whilst the Program, using immunochemical faecal occult blood test for primary screening, improves efficiency of colonoscopy utilisation, only 4% of subsequent colonoscopies are found to harbour cancer. High risk genetic and phenotypic syndromes have specialised and intensive surveillance recommendations, but cumulatively make up only a small proportion of those at risk of CRC. There is therefore a need for improved CRC risk stratification to individualise specific screening strategies as applied to the wider population.

CRC occurs by a complex and little understood interaction between genetic and environmental factors. Outside of high risk Mendelian genetic syndromes, most genetic risk stratification currently occurs on the basis of family history, which is imprecise. Protective genetic factors are also not well identified. Greater ability to refine genetic risks by identifying low penetrance genetic polymorphisms have had limited value in individual predictions due to complex multifactorial effects. Environmental predispositions include dietary factors, smoking and co-morbidities such as obesity, type 2 diabetes mellitus and ischaemic heart disease, many of which are aetiologically and genetically interrelated. Medications such as aspirin and NSAIDs are also known to modify risk.

Whilst high precision risk stratification remains very appealing, this will require complex genetic analyses, thorough behavioural and clinical categorisation and a clear understanding of the interactions of these factors in CRC pathogenesis at the individual level.