**4.3 Disease surveillance, management of residual/recurrent disease**

Close follow-up for NPC patients is essential in terms of disease surveillance. Despite relatively desirable treatment outcomes among solid cancers, unfortunately, about 10-20% of NPC patients will suffer from residual disease or develop recurrent disease after primary treatment, T4 disease among them is reported with up to 45% local recurrence rate [43, 63–67]. Early detection is critical given that extent of relapse determines the chance of salvage, and patients with T1-T2 recurrent disease are more likely to achieve long-term benefit [68, 69]. Initial assessment of residual disease is usually conducted at 12 weeks after the completion of RT or CRT [70, 71]. A detailed history and physical examination, nasopharyngoscopy (with/without biopsy), and radiation imaging (CT/MRI/18F-FDG-PET-CT) are highly recommended in a comprehensive response assessment. Recently, the posttreatment plasma EBV DNA is considered for monitoring for NPC in the context of locoregional failure, distant metastasis, and survival [72].

Emerging evidence suggests that aggressive salvage modalities might increase the chances of better prognosis among patients with recurrent NPC [68, 73, 74]. Neck dissection is widely recommended for isolated regional failure. Re-irradiation is considered for a tumor that recurs more than one year after the completion of primary RT. In contrast, salvage surgery is esteemed if the one recurs within one year and is resectable.
