PROCR and nasopharyngeal carcinoma: In our attempt to identify CSC markers in NPC, we compared biopsy samples from NPC patients at different tumor-node-metastasis (TNM) stages, and found that the epithelial cell adhesion molecule (EPCAM)+PROCR+ cell population could be distinguished from other cell subtypes by their overrepresentation in specimens with advanced disease stage (Fig. 1a).