Objectives: We studied oral cancer incidence and mortality and the impact of compliance to repeat screening rounds during a 15-year follow-up in a cluster-randomized controlled trial in Trivandrum district, Kerala, India.

Methods: Healthy individuals aged 35 and above in seven clusters randomized to the intervention arm received four rounds of oral visual inspection by trained health workers at 3-year intervals, and those in six clusters randomized to the control arm received routine care during 1996-2005 and one round of visual screening during 2006-2009. Screen-positive persons were referred for diagnosis and treatment. Oral cancer incidence and mortality were compared between the study arms by intention to treat analysis.

Results: Of the 96,517 eligible subjects in the intervention arm, 25,144 (26.1%) had one, 22,382 (23.2%) had two, 22,008 (22.8%) had three and 19,288 (20.0%) had four rounds of screening. Of the 95,356 eligible subjects in the control group 43,992 (46.1%) received one round of screening. Although the 12% reduction in oral cancer mortality in all individuals did not reach statistical significance, there was a 24% reduction in oral cancer mortality (95% CI 3-40%) in users of tobacco and/or alcohol in the intervention arm after 4-rounds of screening; there was 38% reduction in oral cancer incidence (95% CI 8-59%) and 81% reduction in oral cancer mortality (95% CI 69-89%) in tobacco and/or alcohol users adhering to four screening rounds.

Conclusion: Sustained reduction in oral cancer mortality during the 15-year follow-up, with larger reductions in those adhering to repeated screening rounds support the introduction of population-based screening programs targeting users of smoking or chewing tobacco or alcohol or both in high-incidence countries.