Abstract
Colorectal cancer is the third most diagnosed cancer worldwide with an estimated 1.93 million cases diagnosed in 2020. Over the past few decades there has been a dramatic rise in the incidence of early onset colorectal cancer, defined as colorectal cancer diagnosed in those aged under 50 years. The largest predictor of survival is early stage at diagnosis, therefore ways to improve prompt diagnosis of early onset colorectal cancer at an early stage is an effective way of managing the impact of this rising disease. Diagnosing colorectal cancer in younger patients has unique challenges with patients falling outside the age of most screening programs and early symptoms of colorectal cancer being common, non-specific and initially intermittent. While colonoscopy remains the gold standard investigation, it is a limited and expensive resource, and current patterns of practice result in large numbers of patients being scoped unnecessarily. The development and use of new and novel non-invasive biomarkers may help (either alone or in combination) identify either symptomatic patients in primary care, or aid with screening asymptomatic patients to focus resources where they are needed most. This review discusses challenges around diagnosing early onset colorectal cancer, with an overview of both current and future methods that might help overcome these challenges. These include increased assessment of familial risk, and the measurement of different biomarkers including faecal haemoglobin, markers of inflammation, gut microbiota, and selected metabolites.