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

Objectives: To examine the optimal screening interval among the individuals who received a negative Epstein-Barr virus immunoglobulin A antibodies against viral capsid antigen (VCA-IgA) serum test result and who comprised the majority of the population screened for nasopharyngeal carcinoma (NPC).
Methods: Screening was performed in Sihui, Guangdong, China, offering a repeated screening for participants with an initial negative test either after 4-5 years in one centre (short interval centre), or 9-10 years in another (long interval centre). The characteristics and incidence rates (IRs) of interval NPCs (defined as cases diagnosed outside the screening protocol while within the screening interval) were compared between these two centres. Standard incidence ratios (SIRs) were also calculated using the general Sihui population as the reference.
Results: Seven interval NPCs were detected in the short interval centre (IR: 17.8/10(5) person-years) and 20 in the long interval centre (IR: 20.8/10(5) person-years during the first four years and 43.5/10(5) 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.