Abstract PS5-07-19: ECOG-ACRIN tomosynthesis mammographic imaging screening trial (TMIST): Update for 2025

Abstract Background: The ECOG-ACRIN Tomosynthesis Mammographic Imaging Screening Trial is a clinical trial being conducted to determine if tomosynthesis (TM) should replace digital mammography (DM) for breast cancer screening based on the impact of the use of each technology on the number of advanced breast cancers in the population of women being screened over several years. If TM is better at finding the types of cancers that are most likely to lead to mortality, the population screened with TM would be expected to have fewer of these types of cancers over time compared with the population screened with DM. TMIST also includes secondary aims in the areas of imaging assessment, medical physics, breast biology and pathology, long-term follow-up, and health care utilization. Besides collection of demographic and clinical information, the study also has a collection of TM and DM screening mammograms, blood and buccal samples, and pathology diagnostic slides and tissue blocks. Methods: Asymptomatic women ages 45 to 74 were enrolled into TMIST across 133 sites located in the United States, Canada, Argentina, Italy, Peru, Chile, South Korea, Spain, Taiwan, and Thailand. At the time of enrollment, women were randomized to undergo screening mammography with either TM or DM annually or biennially based on risk factors for their first 5 years on the study with up to 3 additional years of long-term follow-up under their routine breast screening protocols. Pathology materials for all enrolled women who undergo biopsy or surgery are being collected. Tissue blocks collected will undergo PAM-50 analysis, plus an immune signature. TMIST participants also voluntarily can contribute blood and/or buccal smears to the TMIST biorepository. Update: TMIST met the study accrual goal of 108,508 in December 2024. 21% of the United States participants are African American, with 49% Hispanic participation worldwide. 68.1% of TMIST participants have opted to provide buccal smears, and 66.5% have opted to provide blood to the biorepository. The study will complete follow-up in December 2027. Two ancillary studies not dependent on study endpoints with separate external funding are underway. The first active ancillary project is a study aimed at increasing participation of African American TMIST participants in the biospecimen sub-study of TMIST. New educational materials were developed to provide more information about the purpose of biospecimen collection within TMIST and the process of collecting blood and buccal samples. We are tracking the number of women approached with the new information and providing a patient incentive for those participants who re-consent and provide the samples in this sub-study. Three sites are currently participating that have large numbers of African American TMIST participants who initially declined to participate in the biospecimen collection sub-study. The first site began approaching eligible TMIST participants in April 2025. The sub-study continues through 2026. The second active ancillary project utilizes a case-control design to determine whether lower compression pressure applied during screening mammography correlates with interval cancers. The study is the first in TMIST to utilize selected imaging data and limited clinical information in a protected enclave. No images or data leave EA systems, with an external algorithm being applied to images by staff managing the TMIST imaging archive and statistical analysis being performed by the EA TMIST statistical team. There are multiple additional ancillary projects that are in development that are using TMIST data to 1) estimate the value of AI algorithms that predict short-term risk of breast cancer, 2) assess the rate of overdiagnosis, and 3) aid in the development of individualized screening recommendations (which also will use data from All of US), and others. Citation Format: E. Pisano, C. Gatsonis, M. D. Schnall, M. A. Troester, E. Cole, J. Cormack, J. Steingrimsson, I. F. Gareen, M. Yaffe, L. C. Collins, A. Curtis, R. Carlos, K. D. Miller, C. Comstock. ECOG-ACRIN tomosynthesis mammographic imaging screening trial (TMIST): Update for 2025 [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS5-07-19.