Although the genetic bases of most hereditary cancer syndromes are known,and genetic tests are available for them,the incidence of the most rare of these syndromes is likely underestimated,partially because the clinical expression is neither fully understood nor easily diagnosed due to the variable and complex expressivity. The clinical features of a small pool of rare cancer syndromes include gastroenterological signs,though not necessarily tumors,that could require the intervention of a gastroenterologist during any of the phases of the clinical management. Herein we will attempt to spread the knowledge on these rare syndromes by summarizing the phenotype and genetic basis,and revising the peculiar gastroenterological signs whose underlying role in these rare hereditary cancer syndromes is often neglected. Close collaboration between geneticists and gastroenterologists could facilitate both the early identification of patients or relatives at-risk and the planning of multidisciplinary and tailored management of these subjects. Although the genetic bases of most hereditary cancer are known for, and the genetic tests are available for them, the incidence of the most rare of these syndromes is likely underestimated, partially because the clinical expression is not fully supported nor easily diagnosed due to the variable and The clinical features of a small pool of rare cancer syndromes include gastroenterological signs, though not necessarily tumors, that could require the intervention of a gastroenterologist during any of the phases of the clinical management. Herein we will attempt to spread the knowledge on these rare syndromes by summarizing the phenotype and genetic basis, and revising the peculiar gastroenterological signs of underlying role in these rare hereditary cancer syndromes is often neglected. Close collaboration between geneticists and gastroenterologists could facilitate both the early identification of patients or relatives at-risk and the planning of multidisciplinar y and tailored management of these subjects.