A Question of Equipoise

Posted on: March 22nd, 2019 by admin

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Last week, Etta Pisano, who is chief research officer at the American College of Radiology, sat down for an interview with the editor of The Cancer Letter. They were discussing the Tomosynthesis Mammographic Imaging Screening Trial (TMIST), which is a massive randomized trial to understand the early detection of breast cancer. Pisano referred to the study as the “equipoise question,” in which the researchers are asking: Is digital breast tomosynthesis (DBT) better than full-field digital mammography (FFDM) in reducing development of advanced cancer?

Pisano is no stranger to running these large clinical trials, having been principal investigator for a similar study, entitled “Diagnostic performance of digital versus film mammography for breast-cancer screening,” that was published in The New England Journal of Medicine in 2005. In this multi-centre trial of 50,000 women, the investigators showed that FFDM was more accurate than analogue mammography in younger women and those with dense breast tissue. This led to FFDM replacing film-screen mammography as the gold standard, but in the past decade DBT has emerged as a serious contender to replace FFDM for screening.

Pisano (seen left) explained: “As our tools become more and more sensitive, the question now is: If mammogram technology advances allow us to keep finding more and more cancers, are we further reducing breast cancer mortality?” She continued: “I think some radiologists believe that the more cancers we find, the more lives are saved. However, that may not be true for slow-growing tumours or tumours that cannot be treated effectively regardless of size.”

When the investigators sat down to plan their project, which is funded by the National Cancer Institute, they had to decide on the number of women to enrol. Based on prior research and the size effect they were looking for, the statisticians came up with a figure of 165,000. To date only 9,000 women have been recruited, but Pisano is optimistic that by increasing the number of study sites and hiring on-site research coordinators, their target will be reached within the next few years.

While there have been numerous studies published recently that have shown DBT (seen right) detects more cancers than FFDM, the TMIST trial – which was designed to follow women for 4.5 years – will test the hypothesis: There will be fewer advanced cancers over time in the DBT arm of the trial, compared to the FFDM arm, because the DBT arm will discover those cancers before they grow to become advanced cancers. Science advances slowly but, in time, we should have an answer to the equipoise question.

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