Objectives Robust evidence on the benefits and harms of breast density notification is required to inform future mammography screening policy and practice. This randomised controlled trial (RCT) aims to assess the effect of notifying women with dense breasts participating in population-based breast cancer screening in Australia of their breast density on their psychosocial outcomes and health services use; and to determine whether using different modes of communication alters these effects.

Method Co-designed prospective 3-arm RCT: standard care (no notification of breast density) vs. notification of breast density plus a hard-copy written health literacy sensitive information vs. notification of breast density plus a link to online written and video-based health literacy sensitive information. Women attending for mammography screening, at a single service with multiple sites in Queensland Australia, who are classified as having dense breasts (BI-RADS density C and D) will be randomised. Primary outcome measures will be psychological and health service use. Secondary outcome measures will be cancer worry, perceived risk, breast density knowledge, future mammogram screening, and acceptability. Baseline demographic screening data will be collected, and self-report data will be collected from women over a >2-year follow-up period (8-10-week, 12- and 27-month timepoints).

Results The trial has been registered in the Australian New Zealand Clinical Trials Registry ACTRN12623000001695p and ethics has been approved by the Gold Coast Hospital and Health Service Ethics Committee: HREC/2023/QGC/89770. Trial findings will be disseminated through publications and presentations in national and international peer-reviewed journals and conferences, and reports to relevant government, cancer, and screening stakeholders.

Conclusions This will be the first service-embedded RCT in Australia and the world to test the immediate and downstream impact of breast density notification on women and health services prior to systemic implementation. It will provide evidence to help minimise potential harms including overdiagnosis and map out consequences. Findings will inform Australia’s current and future policy and practice on this controversial issue and may be relevant to screening programs in other countries.