Q&A: Diana L. Miglioretti on breast density and what we’re still learning about DBT

The Patient-Centered Outcomes Research Institute (PCORI) Board of Governors recently approved $7.5 million in funding for a clinical effectiveness research study led by Diana L. Miglioretti, PhD, dean’s professor in biostatistics at the University of California, Davis.

The study involves researching the effectiveness of digital breast tomosynthesis (DBT) and MRI when used with mammography for cancer screening.

Miglioretti spoke with RadiologyBusiness.com about the study and a variety of other topics related to women’s imaging.

RadiologyBusiness.com: Congratulations on the $7.5 million in funding from the PCORI Board of Governors. Can you share a bit about the study you and your colleagues will be conducting and what you hope to achieve with the study?

Diana L. Miglioretti, PhD: We will use the Breast Cancer Surveillance Consortium (BCSC), a consortium of six geographically-diverse breast imaging registries with the largest collection of data on breast imaging linked to breast density in the U.S., to evaluate how breast density can be applied to personalize breast cancer screening and preoperative evaluation of an initial breast cancer diagnosis.

We have two aims. Aim No. 1 will compare the effectiveness of breast cancer screening using digital mammography alone versus digital mammography plus supplemental screening with digital breast tomosynthesis or breast magnetic resonance imaging (MRI) by extent of breast density. Aim No. 2 will compare the effectiveness of preoperative MRI versus no MRI by extent of breast density among women with an initial, pathologically confirmed diagnosis of DCIS or invasive breast cancer.

We hope to determine which subgroups of women might benefit from supplemental imaging and which women may not need these new technologies or may even experience increased harms.

What are your thoughts about the impact of DBT as it has grown in popularity in recent years?

Miglioretti: Information on digital breast tomosynthesis is limited, which is why we are conducting this study. Early evidence on tomosynthesis is promising, suggesting a potential increase in cancer detection and a potential decrease in false-positives (that is, additional work-up performed in women without breast cancer). However, most studies have been conducted in Europe, where breast cancer screening is performed very differently, or in single institutions, most of which are academic medical centers. (The majority of women in the U.S. are screened at community-based, non-academic breast imaging facilities.)

In addition, it is not clear whether any increase in cancer detection will result in a decrease in interval cancers (i.e., cancers that are diagnosed between two screens) or advanced cancers, which is what matters for reducing morbidity and mortality from breast cancer. In other words, the increase in cancer detection could just be an increase in overdiagnosis (cancers that would never harm a women in her lifetime) or it could be due to a shift to earlier diagnosis that does not lead to improvements in cancer outcomes.

More and more breast density reporting bills are being passed in states throughout the country. What has been the impact of these bills on women in the U.S.?

Miglioretti: Legislation requires that women be notified if they have dense breasts and that mammography does not work as well in women with dense breasts. However, it is not clear what we should do differently for these women.

Almost half of women of screening age have dense breast tissue, and mammography is still our best tool for detecting cancer early in these women. It is not clear if the benefits of supplemental imaging outweigh the harms in women with dense breasts who are otherwise at average risk of breast cancer, which is why we are conducting this study.

You recommend women at average risk of breast cancer screen every other year between the ages of 50 and 74. Can you touch on why you believe this to be the safest route for most women to take?

Miglioretti: Evidence suggests that benefit-harm tradeoff is better for biennial versus annual screening. In the BCSC, we found that post-menopausal women diagnosed with breast cancer after a biennial screening exam had similar cancer characteristics as those diagnosed after annual screening, suggesting little or no added benefit of more frequent screening. However, the number of false positive screens is almost double for biennial screeners.

In addition, evidence suggests more frequent screening increases the chance of having been diagnosed with a breast cancer that would have never harmed a women in her lifetime (that is, overdiagnosis).  

Pre-menopausal women are less likely to benefit from screening, so guidelines suggest the decision to screen in this age group should be a personal choice. However, women who do choose to be screened may want to be screened annually because tumors may grow faster in younger, pre-menopausal women. We found that pre-menopausal women diagnosed with breast cancer after an annual screen had more favorable prognostic characteristics than women screened every other year. However, this benefit should be weighed against the increased harms associated with more frequent screening (for example, false-positive exams and overdiagnosis).

This text was edited for space and clarity.