C4A and nasopharyngeal carcinoma: Comprehensive serological evaluation of 99 NPC patients demonstrated distinct immunological patterns between EBERs-positive and EBERs-negative cohorts, with the EBERs-positive group showing non-significant trends toward decreased IgG, IgM, and complement C4, along with elevated IgA and C3 levels compared to EBERs-negative patients (Fig. 4A).