“…Some of the best evidence for a unique biology for AYA CRC compared with CRC in older adults includes more advanced tumor stage at diagnosis, a greater frequency of mucinous histology and signet-ring cells, high microsatellite instability (MSI) and mutations of mismatch repair (MMR) genes [32,34,35,[78][79][80]. Although several publications over the last two decades support the observation of poorer clinical outcomes for younger (<30 years old) patients compared with older adults [20][21][22]25,26,31,[33][34][35][36], these data are difficult to interpret. First, most of these reports are retrospective reviews of small numbers of patients that span a decade or more, making evaluations of treatment approaches difficult (Table 1).…”