Preliminary results of the Digital Mammographic Imaging Screening Trial (DMIST), one of the largest cancer screening trials ever conducted by radiologists, were published September 16, 2005 by the New England Journal of Medicine and at a meeting of the American College of Radiology Imaging Network (ACRIN). This large-scale, multi-center clinical trial was designed to measure differences in diagnostic accuracy between digital mammography and film mammography, an x-ray examination used to screen for breast cancer.

DMIST results showed that, for the entire population of women studied, digital and film mammography had very similar screening accuracy. However, the study revealed that digital mammography was significantly better in screening women in three categories, such as those:

• under age 50 (no matter what level of breast tissue density they had).
• of any age with very dense or extremely dense breasts.
• of any age who are pre- or peri-menopausal women (defined as women who had a final menstrual period within 12 months of their mammograms).

The study's results suggest that for women who fall into these three subgroups, digital mammography may be better than conventional film mammography at detecting breast cancer.

Considerations for Women Seeking Mammography

DMIST showed that there is no apparent benefit of digital mammography over film mammography for women who:

• are over age 50.
• do not have dense or very dense breast tissue.
• are no longer menstruating.

Women who fit these categories should continue to undergo screening mammography per the advice of their physician and the guidelines of national health organizations (see below).

According to the DMIST trial results, women under age 50 (regardless of breast tissue density), women of any age with very or extremely dense breasts and pre-and peri-menopausal women of any age are likely to benefit from earlier detection of breast cancer if they undergo digital mammography instead of film mammography.

However, only 8 percent of breast imaging units in the United States currently provide digital mammography. Women who would like to have digital mammograms can ask their doctors or contact local hospitals or imaging centers to determine if digital mammography is available in their area.

It is important that women not defer screening with mammography due to a lack of access to digital mammography. Film mammography has been successfully used for over 35 years and continues to be the best screening tool for breast cancer available.

The National Cancer Institute recommends that:

• Women age 40 and over should be screened every one to two years with mammography.
• Women who are at a higher than average risk for breast cancer should seek expert medical advice about whether they should begin screening before age 40 and how often they should undergo a screening mammogram.

About the Trial

Begun in October 2001, DMIST enrolled 49,528 women at 33 sites in the United States and Canada who had no signs of breast cancer. Participants had both digital and film mammograms interpreted by two different certified radiologists and were asked to return in one year for their annual mammogram. Breast cancer diagnoses were confirmed by a breast biopsy performed within 15 months after a participant's entry into the study or a follow-up mammogram performed at least 10 months after entry into the study.

The American College of Radiology Imaging Network (ACRIN) coordinated the study. ACRIN, a Cooperative Group sponsored by the Division of Cancer Treatment and Diagnosis at the National Cancer Institute (NCI), is a network of physicians, scientists, and medical institutions that have joined together to conduct clinical trials of new medical imaging technologies. The DMIST was led by Etta D. Pisano, M.D., of the Department of Radiology and Biomedical Engineering, the Biomedical Research Imaging Center and the Lineberger Comprehensive Cancer Center of the University of North Carolina at Chapel Hill.

The Need for DMIST

DMIST is one of several major studies currently underway to determine whether other diagnostic modalities, including digital mammography, can contribute to the early detection of cancer and prevent deaths from the disease. It is estimated that 211,240 women will be diagnosed with breast cancer in the United States this year, and that more than 40,000 will die of the disease.

Death rates from breast cancer have been declining since 1990; a decrease believed to be the result, in part, of earlier detection and improved treatment. However, mammograms do not detect all cancers. Studies have suggested that approximately 10 to 20 percent of breast cancers detected by breast self- or physical examination are not visible on film mammography. The sensitivity of film mammography is somewhat limited in women with dense breasts, which is a population at higher risk for breast cancer. DMIST and other studies are trying to determine what technologies can effectively supplement mammography, especially for high-risk women.

Cancer Detection during DMIST

During the course of DMIST, including the initial screening and follow-up, 335 women were diagnosed with cancer. In general, cancers detected by either film or digital mammography were similar in microscopic structure and stage (how advanced they were).

However, digital mammography detected more advanced or serious breast cancers in women under age 50, women with dense or extremely dense breasts, and in pre- and peri-menopausal women. Lesions missed by film mammography but detected by digital mammography within these three subgroups included many invasive cancers and medium- and high-grade in situ lesions.

In situ lesions in the breast are those confined to the breast duct without invading the surrounding breast tissue and are known as ductal carcinoma in situ (DCIS). Many of these cancers were confined to the breast at diagnosis and had not yet spread to the lymph nodes under the arm. These are lesions that must be detected early to save more lives through screening.

Additional Results of DMIST

Secondary goals of the DMIST study include measurement of the:

• Relative cost-effectiveness of both digital and film technologies; digital systems currently cost approximately 1.5 to 4 times more than film systems.
• Effect on participant quality of life due to the expected reduction of false positive test results.

The results of these parts of the study are still under analysis and will be presented at a later date.