Fig. 1.

Identification of an NPC cell group with stem cell-like properties. a Flow cytometry analysis of CD45^-EPCAM⁺PROCR⁺ cells in different patients with NPC. b Correlation analysis of the amount of CD45^-EPCAM⁺PROCR⁺ cells with the matching TNM stages of the patients (n = 51). c Sphere formation assay of the sorted cells from NPC biopsy samples. All the sorted cells were gated from the CD45⁻ population. *P < 0.05. d Immunofluorescence staining of CD31 and PROCR in sectioned paraffin embedded NPC biopsy samples. e Summary of the xenograft results showing the number of sorted cells transplanted into the mice, and their corresponding engraftment efficiency. The successfully engrafted tumor was regarded as the ones with both osteolytic lesion and lung nodules in mice. All of the successfully engrafted specimens from different patients were pooled together. The CSC frequency is estimated to be 1/17152 according to Extreme Limiting Dilution Analysis (ELDA) with 0.95 confidence interval. f CT scanning of the mice femurs. The image shows the three-dimensional volume reconstruction of leg bones of a representative recipient mouse. The arrowheads label the osteolytic lesions resulting from tumor metastasis. g Lung metastases of the recipient mouse. The arrowheads mark the nodules in the lung, after incubating in the Bousin solution. h HE staining and KI67 expression of xenograft tumors in mouse lungs sections. The right panels show the red box regions at a higher magnification