Background: Colorectal cancer (CRC) is preventable and curable through screening, yet many cases in low- and middle-income countries go undiagnosed or are detected late, leading to poor outcomes. In Nuevo León, Mexico, CRC is the second leading cause of cancer death, but few screening programs have been implemented. In 2022, ISSSTELEON, a local integrated healthcare system, committed to implementing an effective screening program.
 
Objective: To adapt and implement a comprehensive FIT (fecal immunochemical test)-based CRC screening program within a healthcare system in Mexico.
 
Methods: The study was conducted at ISSSTELEON's Monterrey medical center, serving 9,850 adults aged 50-75. Recruitment and education strategies were identified through stakeholder-engaged participatory research. Three hundred average-risk policyholders were randomly selected and invited via email, automated phone call, and navigation call at two-week intervals. During recruitment appointments, trained primary care doctors provided CRC education using validated materials, obtained informed consent, and administered FIT tests. Abnormal results were defined as ≥20 ng hemoglobin/mL. Participants with positive FIT results were referred for diagnostic colonoscopy. Intervention adaptations were documented using the Framework for Reporting Adaptations and Modifications-Expanded (FRAME).
 
Results: Close to half of the selected men and women (142/292; 49%) were reached and scheduled for program recruitment and enrollment. Of these, 9% (13/142) scheduled the appointment after receiving the email, 9% (12/142) after the automated call, and 82% (117/142) after the navigation call. A total of 78% (111/142) of participants attended their recruitment appointment, and among them 83% (92/111) accepted a FIT kit. The mean age (SD) was 60.1 (8.3) years, and 87% (80/92) returned their FIT. We found abnormal FIT results in 10% (8/80) of participants. Colonoscopies were performed in 5 out of the 8 with an abnormal FIT. Polyps were found and removed in all participants with a colonoscopy, and advanced adenomas in most patients (3/5). We documented 21 adaptations to the program. Most of them occurred during pre-implementation (14/21), while the rest were reactive during implementation. The most common modifications were related to the context, specifically the type of personnel that was involved in performing an activity (10/21). For example, outreach (navigation) was conducted by call center personnel and enrollment by a primary care physician, rather than by health promoters. Most common adaptation goals were to increase reach or engagement (7/21), followed by improving feasibility for the clinic staff (6/21). For example, making a second navigation call to patients who did not attend their recruitment appointment, and delivering normal FIT results through the health system's mobile application (to reduce burden on clinic staff in anticipation of program scale-up), respectively. Finally, most adaptations involved discussions with multiple members of the clinical team involved in the implementation process  
 
Conclusions: Collaboratively adapting and implementing an evidence-based colorectal cancer screening program in Mexico allowed the program to be successful. The program incorporated adaptations in participant recruitment strategies, educational materials, and follow-up strategies that could also enhance opportunities for successful implementation in similar settings in Mexico and beyond.