CTSD and nasopharyngeal carcinoma: The results showed that median serum CTSB was 12.5 ± 3.5 mg/L in the NPC group and 2.5 ± 1.4 mg/L in the healthy control; while CTSD concentration was 15.7 ± 8.7 mg/L in the NPC group and 2.7 ± 0.8 mg/L in the healthy control population.