Colorectal cancer (CRC) is the third leading cancer diagnosed globally and an important cause of cancer-related mortality. Of interest, while we have witnessed a declining incidence trend over the past few decades in the older population, incidence rates for adolescents and young adults have been increasing steadily. Several factors may well explain this apparent epidemic in the young, namely a lack of routine screening and emerging lifestyle issues such as obesity, lack of exercise, and dietary factors. It is known that both environmental and genetic factors can increase the likelihood of developing CRC. Although inherited susceptibility is associated with the most striking increases in risk, and must always be considered in a young patient with CRC, the majority of CRCs are in fact sporadic rather than familial. Early-onset CRC is a truly heterogeneous disease, with mounting evidence to suggest that this patient population has a distinctive molecular profile, very different to late-onset CRC cases. Currently, both younger and older patients with CRC are treated in essentially the same manner, but with a better understanding of the molecular mechanisms underlying CRC in the young, we will have the opportunity to specifically tailor screening and clinical management strategies in this unique patient population in an effort to improve outcomes. The aim of this review is to outline our current knowledge of the distinguishing features of early-onset CRC, the ongoing research efforts, and the evolving evidence in this field.
Keywords: Chromosomal instability; CpG island methylator phenotype; Early-onset colorectal cancer; Epidemiology; Hereditary syndromes; Lynch syndrome; Microsatellite instability; Nonhereditary risk factors; Screening; Sporadic early-onset colorectal cancer.