IDO1 and adenocarcinoma: On the other hand, the finding of a low immunohistochemical expression of IDO1, statistically associated with a low Kyn/Trp ratio among NSCLC adenocarcinomas group, corroborated the need for preliminary histopathological screening to identify patients going to serum Kyn/Trp determination, to distinguish those that really could benefit from a blockade of Kyn pathway.