PDCD1 and non-small cell lung carcinoma: The absence of statistically significant associations between a high or low Kyn/Trp ratio, and high or low immunohistochemical expression of PD-L1, in the whole NSCLC population, or within the two histotype subgroups, suggests that these two markers should be carefully considered in the stratification of patients to be treated with an immunotherapy combining the inhibition of IDO1 and the blockade of programmed cell death-1 (PD-1)/PD-L1 interaction.