Breast cancer is the most common cancer among women in Singapore, accounting for nearly 30% of all female cancers. While regular biennial mammography can reduce mortality, screening rates in Singapore remain low at 34.7%; well below the 70% threshold required for population-level impact. Despite a national screening program in place since 2002, uptake continues to be hindered by psychological, cultural, and logistical barriers. Although various studies have explored different behavioural interventions to boost mammogram uptake; ranging from reminders (traditional mailers, phone calls, text messages) and education to financial incentives, their effectiveness varies by population and context. Furthermore, few large-scale, prospective studies have been conducted locally. Prior research in Singapore is either outdated or limited in scope, and there is a particular lack of rigorous trials evaluating behavioral interventions tailored to women who have defaulted on screening, who faces distinct psychological and behavioral barriers; ranging from low perceived risk and fear, to false reassurance from prior normal results or lack of reminders, or had bad experience (procedural pain or prior false positive results) during last mammogram. Engaging these women is critical, yet challenging, and failure to do so undermines efforts to achieve broad population coverage.

The REMIND Study addresses this critical gap by evaluating five pragmatic and scalable outreach strategies to increase mammogram uptake among women who had their last screening more than 2 years ago and are currently overdue. Through a large, randomized controlled trial, the study will generate much-needed local evidence on what works to reengage these women. Findings will directly inform national screening policies and the design of future outreach efforts tailored to Singapore's diverse population.

The REMIND Study is a five-arm randomized controlled trial (RCT) designed to evaluate the effectiveness of a few behavioral interventions to increase mammogram uptake among women aged 50-69 years who have defaulted on mammogram screening. The study's specific aim is to identify effective, affordable, and scalable behavioral interventions that can be implemented in Singapore's general population to improve participation in surveillance mammography. This is a minimal-risk, population-based study that does not require participant visits or in-person interaction, except for a subset involved in a follow-up telephone survey.

Eligibility Criteria: Singaporean women, aged 50-69, who are eligible for free biennial mammograms, with no history of prior breast cancer, have had at least one mammogram before, but not screened in the past 2 years will be will be identified using the NUH electronic medical health records system (EPIC). We will restrict the selection to NUHS patients who are registered users of the NUHS App. To further select/narrow down the eligible participants app activity or last log in date will be used. Patients who signed up the NUHS App have all consented to receive push notifications on research studies. There are over 600,000 registered users of NUHS App. The required 12,750 patients for the study will be randomly selected from these eligible patients.

Randomization and Intervention Arms: A total of 12,750 eligible women will be randomly assigned in equal proportions (n=2,550 per arm) to one of the following five groups:

1. no intervention (control);
2. standard mailed reminder (MR);
3. MR plus a second MR sent four weeks later;
4. MR with a pre-scheduled mammogram appointment; and
5. MR containing behavioral nudge messaging (e.g., social norm or gain or loss framing techniques).

Randomization will be computer-generated. NOTE: Arm 1 represents the current standard practice at NUHS, where patients are not routinely invited or reminded to attend mammogram screenings.

Women in intervention arms 2-5 will receive their respective outreach materials by post (personalized mailers on NCIS letter head) as well as push notifications via the NUHS app. 5-7 days after the mailers are sent, 1st batch of PN will be sent. Up to three batches of PN will be sent to all participants in Arms 2-5, 3 weeks apart. The push notifications will either be linked to a microcontent landing page or a webpage on NCIS website. The content of the mailers and landing page/ webpage will be the same explaining the importance of regular mammography, tailored messages according to each intervention type, and relevant booking instructions or appointment details. These materials have been designed to reflect evidence-based behavioral science strategies and were co-developed in consultation with clinicians, behavioural science experts, and community stakeholders. Participants in the control arm (Arm 1) will not receive any intervention.

This is a minimal-risk study. There are no in-person visits, clinical procedures, or additional tests required. Participation primarily involves receiving reminders. Women may choose to opt out of the study at any time.

Outcome measurement: All data on mammogram completion will be obtained from existing sources such as electronic medical records and the national screening registry. The primary outcome is mammogram uptake within four months of the first intervention (date of sending the mailer/ push notification, which ever is later). In addition to the primary time point, mammogram uptake data may also be extracted at the 6-month and 12-month marks following the intervention. These extended follow-up points will allow for the assessment of any delayed uptake, which may help to understand the longer-term impact of the interventions. No new clinical data will be generated from participants.

NOTE: To avoid a huge surge in calls to the appointment booking hotline number, mailers will be sent in a staggered manner over 4-12 weeks. Hence, the collection of mammogram completion data will also be staggered and will be 4 months from the day of sending the mailers/PNs which ever is the later. Similarly, for the participants in Arm 4 (mailer reminder with pre-scheduled appointment), the mailers/PN will be sent out 4-6 weeks prior to the appointment date and the mammogram completion date will be calculated four months from the date the mailer/PN was sent.

Post-trial telephone survey: In addition post-trial, a subset of participants from Arms 2-5, will be randomly selected to participate in a telephone survey aimed at understanding motivations, barriers, and perceptions related to the interventions and screening. Participants will be randomly selected and contacted until a total of up to 70 participants in each arm responds and takes part in the survey. About 3-8 weeks post trial, the participants will be contacted via phone, and verbal consent will be obtained prior to initiating the survey. They will be informed that the survey will take about 5-10 minutes, their participation is voluntary, they may skip any question or withdraw at any time, and their responses will remain confidential. Trained research staff will be performing the telephone survey.

Inclusion Criteria:

• Singaporean citizen
• Age 50-69
• Registered as a patient at the National University Hospital
• Registered and active user of NUHS App
• Signed up with Healthier SG with a primary care provider within the NUHS Primary Care Network
• Must be defaulted repeat screeners : Must have done one prior mammogram screening but not in the past 2 years

Exclusion Criteria:

• Diagnosis of breast cancer in EPIC
• Mammogram done in the past 24 months in EPIC

Females only