To date, there are no serum biomarkers available for the prediction of recurrent 
nasopharyngeal carcinoma (rNPC). The diagnosis of rNPC mostly depends on imaging 
and biopsy of diseased tissue; however, both of these methods work mostly if the 
target tumor is at an advanced stage. Therefore, the identificaqtion of 
recurrent biomarkers is urgently required. In the present study, we used tandem 
mass tag (TMT) labeling and high performance liquid chromatography (HPLC) 
fractionation followed by liquid chromatography-tandem mass 
spectrometry (LC‑MS/MS) to identify differentially expressed proteins. Serum was 
collected from 40 patients with NPC [recurrence (n=20) and no 
recurrence (n=20)]. Compared to non‑recurrent NPC (nrNPC), we found 59 proteins 
to be significantly dysregulated in rNPC; most of these have been previously 
reported to play a role in carcinogenesis. The dysregulation of 
calmodulin (CALM) was confirmed in 74 new patients [recurrence (n=32) and 
no recurrence (n=42)] by ELISA. Moreover, we performed a preliminary pathway 
analysis which revealed that oxidative phosphorylation was altered in the 
patients with rNPC compared to those with nrNPC. Taken together, these data 
identify a potential diagnostic biomarker for rNPC and elucidate the potential 
molecular mechanisms that are dysregulated and contribute to the pathogenesis of 
rNPC.