IDO1 and leukoplakia: However, our study has several limitations, including, but not limited to: 1) The number of clinical samples for single-cell RNA sequencing was limited; 2) The lack of prognostic data for OLK in the database, as well as the long follow-up time required to obtain prognostic data for leukoplakia in the clinic, results in a lack of clinical evidence for the prognostic impact of IDO1+ macrophages on oral leukoplakia, which needs to be validated in further prospective clinical studies.