The Small Bowel Cancer Incidence Enigma.

Although the small bowel is a vast organ with a highly proliferative epithelium, the incidence of small bowel cancers is surprisingly low. Many factors could be involved in this unexpected cancer incidence, including difficult access to the exploration of the small bowel mucosa, which might lead to missed diagnoses of non-obstructive and non-bleeding small tumours. Moreover, possible factors that influence the low incidence include more efficient machinery of DNA replication and DNA repair enzymes, peculiarities in microbiota components, competence of the immune system, and the speed of intestinal transit. Importantly, the answer for the enigmatic risk of driver mutations caused by replication errors may be hidden in the small bowel, which is an obscure part of digestive tract that is usually inaccessible by endoscopic or colonoscopic conventional investigations. These observations warrant the necessity of an urgent exploration of small bowel features, including the evaluation of DNA replication controls and expression of DNA repair genes, in order to shed light on these obscure events.