Background
Population-based cancer registries (PBCR) are essential for cancer surveillance, planning, and evaluation. In Mexico and other low- and middle-income countries (LMICs), PBCR rely on hybrid workflows in which cases are identified at healthcare facilities but data entry and coding are completed later at registry offices. This fragmented process compromises data timeliness, completeness, and quality, while increasing registrar workload.
CanReg5, an open-source software developed by the International Agency for Research on Cancer (IARC), supports standardized case capture, storage, quality control, and analysis. Although widely used in LMICs, its implementation remains largely office-based, limiting the potential of digital health tools to strengthen field-based data collection. In Mexico, PBCR operate through 10 sentinel nodes covering more than 1,300 data sources, where delayed office-based registration increases the risk of duplicate or incomplete records and reduces productivity and data quality.

Objectives
To describe the development of a mobile application designed to enable cancer registrars in Mexico to capture and update CanReg5 data directly at the data source, improving efficiency, data quality, and registry performance.

Methods
Using an implementation-oriented, user-centered design approach, a mobile application was developed to enable registrars to securely query the registry database onsite to determine whether a case is new or previously registered and to capture or update information directly at the data source. It was developed using Kotlin for Android devices with online functionality. Data security is supported through role-based user authentication with username and password, end-to-end encrypted communication over HTTPS, and application-level request validation using one-time password (OTP) mechanisms. Secure data synchronization with the central CanReg5 database is conducted via WebSockets and HTTPS.

Results
The Android-based mobile application incorporates 26 variables organized into three modules: (a) patient information (name, sex, date and place of birth, residence, vital status, date of last contact); (b) tumor information (incidence date, age at diagnosis, topography, morphology, extent, laterality, metastasis, stage); and (c) source information (source name, source type, medical record or identification number). Data entry combines free-text fields and predefined drop-down lists, reducing coding errors and improving standardization.
The tool was reviewed by institutional information systems teams, whose feedback informed iterative refinements. A pilot implementation was conducted in three PBCR—one each in northern, central, and southern Mexico— 56 cases were captured and subsequently validated in CanReg5. Real-time case verification enabled registrars to distinguish new cases from updates, minimizing duplication and unnecessary re-abstraction, and improving productivity, data quality, and completeness by eliminating delays associated with office-based data entry.
Currently, case searches are performed using the national personal identification code (CURP), with name-based search under development. The application is available for Android devices only, with data connectivity costs covered by registrars. The next phase involves deployment across all ten sentinel PBCR.
 
Conclusions
This mobile application represents a digital health strategy to strengthen PBCR in a middle-income country. The approach demonstrates the potential of mobile technologies to support cancer surveillance capacity building and scalability to other registries and LMICs, while reducing registration time and improving registrar productivity, data quality, and completeness.