QSOX1 and nasopharyngeal carcinoma: In our previous study, we analyzed the total secretory protein profiles in NPC cell lines with variable radiosensitivities and compared the conditioned serum-free medium of radioresistant CNE-2R cells with that of the parental radiosensitive CNE-2 cells using isobaric tags for relative and absolute quantitation (iTRAQ) with liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS/MS) quantitative proteomics and found that the expression of quiescin sulfhydryl oxidase 1 (QSOX1) was significantly different between these cell lines [8].