A large-scale clinical trial funded by the National Cancer Institute aims to determine whether three-dimensional mammography is more effective than two-dimensional mammography and whether it is more or less likely to result in false positives.

The Tomosynthesis Mammographic Imaging Screening Trial (TMIST) will be conducted by the ECOG-ACRIN Cancer Research Group, with the backing of NCI, which is part of the National Institutes of Health in the Department of Health and Human Services. The researchers are beginning to enroll the first of an estimated 165,000 women who will participate in the study through 2020; they will continue monitoring them through 2025.

Tomosynthesis is the scientific name for a radiology technique through which multiple mammography images are assembled into a single digital rendering, showing more perspectives on breast tissue. The goal is to spot tumors that otherwise might have been missed. However, the technology has not been universally welcomed as the new standard of care. Critics say 3D scans may be more likely to result in biopsies and treatment of small tumors that never would have grown to be life-threatening, causing women unnecessary alarm and expense.

TMIST will seek more definitive answers to these questions, based on a study that includes about 100 clinics in the United States. Several clinics in Canada that were part of an earlier related study will also participate.

“Nearly 50 million screening mammograms occur each year in the United States, yet it has been decades since a large-scale randomized trial of mammography has been done,” says Worta McCaskill-Stevens, MD, director of the NCI program supporting the trial. “The evolution of mammography technology provides us with an opportunity to fill in the gaps in our knowledge about two available breast cancer screening tests.”

Women between the ages of 45 and 74 who plan to get routine mammograms are eligible to enroll. They will be assigned randomly to either the 2D or 3D mammography group for a period of five years. Researchers will be watching to determine how frequently the scans result in follow-up testing or a diagnosis of breast cancer, and whether the outcomes for either group are better than the other. Beyond spotting tumors, they want to know whether the technology is effective at spotting the types of tumors most likely to spread and kill women.

As a newer technology, tomosynthesis is more expensive than traditional 2D mammography, although insurance coverage for the procedure is becoming more common. The TMIST trial could help provide answers to whether it is worth the money and the effort.

Even if the procedure does not make sense for everyone, TMIST will test whether it might make sense for specific groups of women. According to NCI researchers, questions they hope to answer include:

  • Among the women who receive 3D mammography, will there be fewer harder-to-treat cancers in certain groups, such as those with dense breasts, African Americans, premenopausal women, and women on hormone replacement therapy?
  • Will there be fewer false-positive test results in the entire study group or among certain groups?
  • Is there a link between certain findings from the mammograms and the most aggressive breast cancers?

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