Digital mammography detects more cancers than film-screen mammography in young women

This paper was published in September 2005 in the New England Journal of Medicine and has received considerable media attention. A review of this paper by staff at Westmead Breast Cancer Institute is provided here.

The study found that in a breast screening setting in North America

• Overall there was no significant difference in the diagnostic accuracy between the two types of mammography, however
• The diagnostic accuracy of digital mammography was significantly higher in the following subgroups:

• premenopausal and perimenopausal women
• women with dense breast tissue
• women under 50 years of age

A review of Pisano ED, Gatsonis C, Hendrick E et al for the Digital Mammographic Imaging Screening Trial (DMIST) Investigators Group. Diagnostic performance of digital versus film mammography for breast cancer screening.
N Engl J Med 2005; 353.

By
Dr M Brennan, Director of Education, Westmead Breast Cancer Institute
A/Prof John Boyages, Executive Director, Westmead Breast Cancer Institute
Date: 21 September 2005

Methods and Results

The paper reports the findings of the DMIST trial, a multicentre trial conducted in the United States and Canada. Almost 50,000 asymptomatic women presenting for mammography screening for breast cancer had both film-screen and digital mammography performed. The films were read independently by two radiologists and the results were compared.

Overall, 335 cancers were detected

Type of cancer

• invasive 231
• DCIS 103
• other 1

Invasive cancers diagnosed on

• both film and digital mammography (all) 85 (women <50—12)
• film mammography alone (all) 35 (women <50—3)
• digital mammography alone (all) 38 (women <50—14)
• neither type of mammography (all) 73 (women <50—14)

DCIS diagnosed on

• both film and digital mammography (all) 36 (women <50—14)
• film mammography alone (all) 17 (women <50—3)
• digital mammography alone (all) 25 (women <50—8)
• neither type of mammography (all) 25 (women <50—4)

These results show that of the 335 cancers in the nearly 50,000 women there were

• 63 cases of cancer picked up on digital mammography that were not seen on conventional film-screen mammography
• 52 cases of cancer picked up on film-screen mammography that were not seen digital mammography
• 121 cases of cancer picked up on both types

(Result did not show a statistically significant difference between two types of mammography p=0.18)

In women under 50 there were

• 22 cases of cancer picked up on digital mammography that were not seen on conventional film-screen mammography
• 6 cases of cancer picked up on film-screen mammography that were not seen digital mammography
• 26 cases of cancer picked up on both types

(Result highly statistically significant difference between two types of mammography p=0.002)

A statistically significant difference was also seen in women who

• were premenopausal or perimenopausal p=0.002
• had dense breast tissue p=0.003

What are the study’s weaknesses?

• accuracy of mammography is evaluated but it is not certain if this will translate into saving lives as mortality was not measured
• while the study cohort was large, the number of cancers in each subgroup is small

What does this study mean for clinical practice?

This study has shown significant results. There has been conflicting evidence of screening benefit in women under the age of 50. This has been thought to be due in part to the lower accuracy of mammography in women with dense breast tissue. This study suggests that digital mammography may be advantageous in these women and may lead to a screening benefit (measured by decreased mortality) in the future.

It is possible that the findings of this research will

• increase funding for digital mammography in the BreastScreen program in Australia
• lead to special (higher) rebates for digital mammography in the diagnostic setting

Final comments

“This is very exciting research” says Professor John Boyages, Executive Director of the Westmead Breast Cancer Institute. “Our Institute was the first in Australia to move to digital mammography. Our anecdotal experience has been that there are huge advantages as the digital images can be manipulated and examined in detail without subjecting the patient to more discomfort and radiation for additional mammographic views. This study supports our experience. The main disadvantage of digital mammography is the enormous cost and this has slowed uptake of the new technology. Hopefully the publication of these results will help in our battle to make this technology more widely available to women in Australia through screening programs,” Professor Boyages adds.

Many women with established breast cancer have requested a digital mammogram for routine follow-up. This was not studied and many women in this group also have an ultrasound and cone-compression and magnification views. In our view, routine mammography +/- work-up views and ultrasound is all that is required at his point in time.

Further background:

What is digital mammography?

Difference from film-screen mammography

• computer used to generate images
• images are seen on a computer screen
• may also be printed on film for viewing on a standard light box

Advantages

• image can be manipulated on a computer screen
• areas of interest can be viewed in more detail without the need for extra mammographic views (and extra discomfort and radiation for the patient)
• multiple copies can easily be printed
• images can be sent to and from different locations, which can be a particular advantage in rural areas
• may be used with CAD- computer aided diagnosis: software that can ‘second-read’ the mammogram and highlight areas of interest for the radiologist to reconsider

Disadvantages

• specialised equipment required
• much more costly than film-screen images: 3-4 times the cost
• large files can create storage problems on computer
• no extra Medicare rebate for digital mammography

Last Updated on Tuesday, 09 February 2010 12:17