ALDH1A1 and neoplasm: In this study, we isolated ALDH1-positive CCSCs from tumor tissues of patients and checked PD-L1 expression in these cells; our results showed that the positive rate of PD-L1 was up to 48.1%, whereas that of non-CCSCs was less than 20%, indicating that PD-L1 expression was high in ALDH1-positive CCSCs.