Interim results from a trial of a new laser technology to diagnose pre-cancerous polyps in the colon indicate the technology works best when used in combination with another specialist endoscopy technique.
The findings, presented during the 2016 United European Gastroenterology Week in Vienna this month, show that combining the WavSTAT Optical Biopsy System® with a technique called narrow band imaging (NBI) creates an examination that is sensitive enough to spot cancer but specific enough not to over-diagnose it.
WavSTAT® connects a fibre optic probe to standard endoscopic biopsy forceps. The device shines light onto the polyp and analyses the fluorescence reflected back from the tissue to determine if it is benign, pre-cancerous or cancerous.
In the trial, WavSTAT® had a higher than 90 per cent negative predictive value, which means when it diagnosed a polyp as benign, it was correct 90 per cent of the time, meeting the international threshold to be a safe and accurate test.
But because it was so sensitive, it also identified a significant number of polyps as pre-cancerous when they were in fact benign. This was particularly an issue in the lower section of the bowel, called the recto-sigmoid, where more benign polyps are usually found. The tissue in this area is usually thicker than elsewhere in the bowel and so more likely to be activated by the WavSTAT® laser.
Dr Venkat Subramanian, Associate Professor and Consultant Gastroenterologist who led the trial at St James’s University Hospital, Leeds, explains: “For a test to be clinically safe, it needs to be sufficiently sensitive to pick up cancerous polyps. But if it is not specific enough, and diagnoses benign polyps as pre-cancerous, that will result in unnecessary treatment for the patient and more cost for the NHS, which makes the test uneconomic.”
Because St James’s is a specialist centre, with the expertise to carry out a range of endoscopic techniques, Dr Subramanian was able to add another element to the trial: narrow band imaging (Olympus, Keymed, UK). This places a filter between the polyp and the white light source used in a standard endoscopy, enabling the clinician to see the surface of the polyp more clearly and so make a more accurate visual diagnosis. NBI is not in wide clinical use as it is only accurate in the hands of clinicians with the appropriate training and expertise.
When Dr Subramanian analysed all the results from the trial, he found that a combination approach produced the best overall balance between sensitivity and specificity: using NBI to double-check a WavSTAT® diagnosis of a pre-cancerous polyp in the rectum and sigmoid, but relying on the WavSTAT® diagnosis alone for other areas of the bowel.
“The ultimate aim is a system that identifies and treats cancerous and pre-cancerous polyps during endoscopy without the need for histopathological analysis – reducing the number of visits patients make to hospital and enabling clinicians to set up appropriate follow up schedule,” says Dr Subramanian. “Our study shows that WavSTAT® has the potential to do this, if combined with a different technology for the recto-sigmoid. We now need a larger study testing this combined approach, to see if we can improve the accuracy of the diagnosis without losing sensitivity.
“Alternatively we can use a different threshold for diagnosis of benign polyps in the rectum and sigmoid when using Wavstat optical biopsy and then clarify if this new threshold improves the specificity without any loss of sensitivity in a further clinical trial.”
Thanks to an introduction made by the HTC between Dr Subramanian and SpectraScience, the San Diego- based medical device company, who developed the WavSTAT® system, St James’s was the only UK hospital to take part in the international, multi-centre trial. The interim results presented by Dr Subramanian are based on findings from the work in Leeds, as each centre enrolled sufficient patients to make their individual results statistically significant. The full findings from the trial are still to be published.
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