Interval cancers in nasopharyngeal carcinoma screening: comparing two screening intervals after a negative initial screening result

person-years during the remaining years). The SIR in the short interval centre was 0.43 (95% confidence interval (CI): 0.17-0.89); SIR in the long interval centre was 0.47 (95% CI: 0.17- 1.02) during the first four years and 0.90 (95% CI: 0.49-1.51) during the remaining years. No aggressive interval NPC was observed in the short interval centre; four were identified in the long interval centre. Conclusions The incidence of NPC, especially aggressive NPC, was low during the first few years after a negative screening; the incidence increased to the general population level afterwards. A screening interval of 4-5 years may therefore be more suitable than 9-10 years after a negative VCA-IgA test in NPC screening.