 Digital
Mammographic Imaging Screening Trial (DMIST) - The
long-awaited study was sponsored by the National Cancer
Institute and published online by the New England Journal of
Medicine. Experts examined the scans of more than 42,000 women
at 33 institutions across the United States and Canada. It was
one of the largest studies ever done comparing digital to film
in medical imaging. For women under age 50, for instance,
digital imaging showed about a 15 percent accuracy advantage
over film, presumably finding cancers at a point when
treatments may be better able to cure the disease. The digital
edge was about 11 percent among women of any age with dense
breasts, which are hard to read with standard film
 equipment,
and 15 percent in women who hadn't yet reached menopause.
Breast cancer is one of the most easily treated forms of
cancer if caught early enough. Widespread use of mammography
to detect lumps -- and even pre-cancerous cellular changes --
is regarded as one of the most successful innovations in
modern public health. Digital offers some obvious advantages
beyond the higher sensitivity for certain groups of patients.
Images made on a computer are easier to store and move from
one medical office to another, for example. Radiation doses
tend to be lower in the digital format with no compromise in
image quality. The study results indicate that only women who
fit in ANY of these three categories would benefit from
digital mammography instead of film mammography:
- under age 50 (regardless of level of
breast tissue density)
- of any age, with heterogeneously
(very dense) or extremely dense breast tissue.
- or pre- or perimenopausal women of
any age (defined as women who had a last menstrual period
within 12 months of their mammograms).
These results suggest that for women who
fall into three subgroups (women under age 50, women with
heterogeneously dense or extremely dense breasts, and pre- and
perimenopausal women), digital mammography may be better at
detecting breast cancer than traditional film mammography.
Approximately 65 percent of the women in DMIST fit into one of
the three subsets that showed a benefit with digital
mammography.
For women, breast cancer is the most
common non-skin cancer and the second leading cause of
cancer-related death in the United States. Death rates from
breast cancer have been declining since 1990, and these
decreases are believed to be the result, in part, of earlier
detection and improved treatment.
Both digital and film mammography had sensitivities (the
ability to tell if a cancer is present) for breast cancer of
70 percent in the overall study population using the
conventional methods for measuring sensitivity in a breast
cancer screening trial. The sensitivity for women with dense
breasts was only 55 percent for film mammography while the
sensitivity for digital mammography was 70 percent. The
overall rate of 70 percent is within the expected rate of
detection. Specificities, or the ability to tell correctly
that a cancer is NOT present when the breasts are normal, were
high for DMIST, just as would be expected of screening
mammography. Using one year follow-up interval, specificities
for both digital and film mammography were 92 percent for the
overall population.
Randomized clinical trials that have
studied mortality have shown a reduction in mortality from
breast cancer with the use of screening mammography, ranging
from 18 percent to 30 percent depending on the age of the
women. DMIST results indicate that screening with digital
mammography will detect at least as many breast cancers as
film mammography over the whole population, and more advanced
or serious breast cancers in women in the three subsets of the
population. This suggests that at least as many -- and
possibly more -- lives will be saved with digital mammography
as are now saved by screening with film mammography.
At present, only 8 percent of the
mammography units in the United States have digital systems,
whereas approximately 40 percent of women undergoing screening
mammography have dense breasts. It will be impossible for all
women who have dense breasts to receive digital mammograms, at
least for the near future. As more digital mammography systems
become available, more women in the groups who are likely to
benefit from digital mammography will have access to this
technology.
The results of these parts of the study
are still under analysis and will be presented at a later
date. In fact, even though a reduction in false positives with
digital mammography was expected, none was found in DMIST. The
effect of false positive results on quality of life will be
reported at a later date.
Reader (radiologist) studies also were
conducted using the mammograms obtained in DMIST. DMIST also
suggested that who reads you're report may also affect your
outcome. |
