A SCANNING technique that highlights the blood vessels that feed growing tumours could help reveal whether breast lumps on mammograms are cancerous. Initial tests suggest it could cut the number of false alarms by 70 per cent, sparing many women from unnecessary biopsies.
Mammograms, simple X-rays that show up denser tissue in the breast, are widely used to screen women over 35 years old for breast cancer. But in recent years the value of mammogram screening has been questioned. Many lumps turn out to be harmless, or mere artefacts of the scanning process. And some cancerous lumps are are so slow-growing that the tumour is best left alone.
In the US, for instance, 8 out of 10 lumps deemed suspicious on the basis of mammograms are found to be cancer-free when a sample is taken with a needle. Such biopsies are an emotional ordeal for the women, and an economic burden for health services such as Britain鈥檚 NHS.
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So DOBI Medical Systems in New Jersey is developing a scanner that could double-check any lumps found on a mammogram, before resorting to a biopsy. The scanner looks for the network of blood vessels feeding tumours with oxygen and nutrients. A fast-growing tumour usually has a dense network of capillaries.
In DOBI鈥檚 machine, the breast is gently squeezed between an array of bright red LEDs and a camera. The pressure (far less than applied in mammograms, which can be painful) squeezes blood out of most of the breast. But some remains trapped in the capillaries of tumours, says Phillip Thomas of DOBI, because they are very different from normal vessels. 鈥淭hey are very tortuous, intertwined like a bird鈥檚 nest.鈥�
Since blood absorbs red light, a cancerous region will show up as a darker splodge in the picture, he says. Although magnetic resonance imaging produces similar images, it is too expensive to use widely.
If the suspicious area on a mammogram matches up with a splodge in the DOBI scan, says Thomas, there is a high likelihood that it is cancer. Preliminary tests comparing DOBI scans with conventional methods in 200 women suggest the scans could cut the number of false alarms by as much as 70 per cent. The results will be presented to a conference in Boston next week.
However, not all types of aggressive cancer are associated with the development of new blood vessels, cautions Martin Yaffe, a breast-imaging specialist at the University of Toronto. Until the scan is proved reliable, it is better to do a biopsy than endanger a life, he says.
It may also be hard to distinguish between harmless and aggressive tumours with a DOBI scan. Although the capillaries clustered around malignant tumours are denser and penetrate deeper than in benign growths, there is a risk of a 鈥渇alse negative鈥�.
Nevertheless, anything that improves the sensitivity of mammography is worth pursuing, says Richard Davies, who has been supervising trials of the DOBI scanner at the Hackensack University Medical Center in New Jersey. It could be especially useful for younger women, because mammography cannot differentiate between tumours and their denser breast tissues, so other techniques such as ultrasound have to be used.
There is also some hope that the DOBI scans could provide an early warning of cancer, revealing speck-sized tumours too small to show up on mammograms. This will be put to the test when clinical trials begin later this year.