Adjusting the TMIST study design to accommodate slower than expected accrual: ECOG-ACRIN EA1151.

TPS10614 Background: The ECOG-ACRIN Tomosynthesis Mammographic Imaging Screening Trial (TMIST), which opened in 2017, is a randomized trial designed to assess whether Tomosynthesis Mammography (TM) should replace Digital Mammography (DM) for breast cancer screening. It is hypothesized that women assigned to TM for 3-5 screening rounds will have fewer advanced breast cancers than the women assigned to DM. Advanced cancers are those that have distant metastases or positive nodes, are invasive tumors greater than or equal to 2.0 cm in size, or are invasive tumors greater than 1.0 cm in size that are triple negative or HER 2+. The initially planned enrollment of 164,946 women was due to be completed by the end of 2020, with follow-up concluded by 2025. There were substantial challenges in meeting this timeline, including the organizational and funding structure of the NCI National Clinical Trials Network which is dependent upon sites using their existing staffing resources (not always readily available at the time of study activation). This led to longer than anticipated start of enrollment for most interested sites and lower than anticipated annual enrollment per participating site based ultimately on the staffing support that could be allocated to manage TMIST. In addition, research staffing shortages and periodic research operations closures due to COVID-19 have also impacted enrolling TMIST sites, though unevenly, since the start of the pandemic. Enrollment plateaued at approximately 2,100 subjects per month by the end of 2020. With that accrual rate expected, the trial design was modified to reduce the sample size so that the study could be completed by 2027. Methods: With the approval of the NCI CIRB, we changed how the primary endpoint measure for TMIST is assessed from the number of advanced cancers that occur by 4.5 years after randomization to the time from randomization to occurrence of advanced cancers. All advanced cancers occurring within 7 years of randomization are now included and all participants followed for at least three years. In addition, the power of the study of the study was modified from 0.9 to 0.85, while the originally assumed effect size at 4.5 years was retained These changes allowed a reduction of sample size to 128,905, with subject recruitment projected to end in 2024. As of February 14, 2022, there are 125 sites open, 114 in the U.S. and 11 in other countries, with an additional 31 sites planning to open. As of February 14, 2022, a total of 63,845 women have been enrolled in the trial worldwide at 115 sites, with 20% of US participants self-identifying as belonging to minority racial and ethnic groups and 70% consenting to optional blood and/or buccal cell collection. Clinical trial information: NCT03233191.