Hi-tech breast-cancer screening: will it deliver?

FEATURE

Hi-tech breast-cancer screening: will it deliver? already been developed for use with n February, full-field digital mamfilm-based mammograms, says Paul mography made the news on both Taylor (University College London, sides of the Atlantic. The UK’s first UK), but the only system currently system was installed at the Princess approved for use in the USA is the R2 Grace Hospital in London, and, in ImageChecker systhe USA, the Food tem. CAD software and Drug is based on algoAdministration rithms that enable (FDA) announced the computer to that it had approved highlight any suspiGeneral Electric’s cious areas that equipment for use could be microcalin US breastcifications, masses, screening proor other signs of grammes. Martin cancer. So will the Yaffe (University of impending switch Toronto, Canada), to digital systems who is hosting the speed up research 5th International “We’re thrilled” says Perry into CAD? Workshop on “Definitely”, says Taylor. “We will Digital Mammography (Toronto; no longer need to digitise a film June 11–14) welcomes both developimage to analyse it, and the images ments. “Although digital mammograwill be ‘cleaner’”. However, he wonphy still needs careful evaluation, it ders whether CAD systems will suroffers significant advantages over vive as independent products: film-based systems”, he says. “Radiologists may well push manuMammographic X-ray techniques facturers to incorporate software into are the same, irrespective of the systhe digital equipment as a ‘ready-totem used. The difference lies in the use’ package”, he predicts. way the image is produced and But will hi-tech digital mammograprocessed. Instead of appearing on an phy and sophisticated CAD software X-ray film, a digital image is prereally improve breast-cancer detecsented on a high-resolution computer tion? “It is tempting to be carried screen. “Whilst the sensitivity of the away with the pace of technological digital system (its ability to detect development”, warns Sue Astley breast cancers) has so far been shown (Manchester University, UK). For to be equal to that of the film-based the last 7 years Astley has been assesssystem, its specificity (the ability to ing how radiologists interpret mamavoid false positive diagnoses) is mograms, both with and without the already better”, explains Yaffe. And help of CAD systems. “No-one has since technology is advancing all the yet proved conclusively that any of time, digital systems will certainly the systems available significantly improve during the next few years. improve the radiologist’s perforNick Perry, Consultant Radiologist mance”, she says. Although the best at the Princess Grace reports that, CAD systems prompt the reader to after 3 months’ use, radiologists there consider areas of interest, those that are already “thrilled” with the full give too many false prompts distract field system. “The most impressive the reader and worsen their detection aspect of the system is the way the rate. Taylor agrees and says that his image can be manipulated; the conown team is developing the CADtrast, density, magnification and oriMIUM system to try to avoid this entation can all be adjusted to problem. “CADMIUM includes optimise the reporting conditions”, some ‘intelligence features’ that he says. The financial outlay is large, inform the radiologist why prompts but the technology will pay for itself have been made. We hope this will within the National Health Service discourage them from ignoring a (NHS) breast-screening programme prompt just because they do not because of the large through-put of understand why the computer has patients. “With the digital system, no made it”, he says. films are used and images can be This is all great news for women transferred and archived electroniolder than 50 years, says Mike Brady cally; on a large scale, savings will be (Oxford University, UK), but not so significant”, he adds. good for premenopausal women. Digital mammography also lends “The breasts of younger women are itself well to computer-aided diagnofull of active parenchymal tissue that sis (CAD). Several systems have

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absorbs X-rays, making the mammogram appear almost completely white”, he explains. Brady thinks that the next challenge for breast-screening technology will be to lower the age of effectiveness, enabling effective screening in women as young as 35. “This will involve using alternative and new techniques, none of which have yet made a significant impact”, he says. Magnetic resonance imaging (MRI) has great potential; it is very sensitive and can be used to detect breast cancers in women of any age. It is particularly useful in women carrying the BRCA1 or BRCA2 mutations, since they often need to be screened for developing breast tumours in their 30s. Nola Hylton, of the Magnetic Resonance Imaging Science Center (University of California, San Francisco, USA) is confident that MRI will be used more in the future. For now, however, the main problem is cost. “It is difficult for most centres to afford a dedicated breast-screening MRI machine, and this limits availability”, she says. Also, although the sensitivity of MRI scanning is good, the specificity is less so, and the scans produce many false positives. Brady agrees, but says that it might be feasible for manufacturers to design a cut-down version of an MRI machine, just for breast screening. Good results on younger women have been obtained using positronemission tomography and singlephoton-emission computed tomography—techniques in which the tumour is identified by its higher uptake of a radiopharmaceutical. “Again, although the image quality is good, both techniques are expensive”, says Brady. Exactly the opposite is true for ultrasonography. “Ultrasonography is cheap and available, but, until very recently, image quality has been poor”, he adds. However, Doppler techniques can now be used to reveal the enhanced blood supply around a tumour and ultrasound to generate three-dimensional representations of the whole breast, and any masses within it. Brady concludes that the advent of full-field digital mammography is going to make a big difference to the over 50s, but for those women who are too young for mammography, “ultrasonography just might surprise everyone”. Kathryn Senior

THE LANCET • Vol 355 • May 20, 2000