Colon cancer: Spectral diagnostic

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  • Published: Nov 1, 2013
  • Author: David Bradley
  • Channels: Raman
thumbnail image: Colon cancer: Spectral diagnostic

Going off-label

Credit: Gerwert et al/Analyst/Royal Society of Chemistry - Stained colon cancer cells, Raman false-colour SHP images

Researchers in Germany have developed a new use for Raman spectroscopy to support pathologists in the diagnosis of cancer. Writing in two parallel papers in the Journal of Biophotonics and the Analyst they compared conventional procedures for detecting colon cancer with their label-free spectroscopic histopathology method.

Klaus Gerwert from the Protein Research Unit Ruhr within Europe (PURE) at Ruhr-Universität Bochum (RUB) and colleagues explain how the approach avoids one of the most inconvenient aspects of current approaches to cancer diagnostics. "Contrary to previous methods we no longer have to stain the tissue in order to detect cancer," explains Gerwert, "In the future, this will give us the opportunity to classify a tissue sample automatically as being either normal or diseased."

Biopsy avoidance

Current histopathology involves obtaining tissue samples via biopsy, slicing the sample into thin sections and then staining them chemically. Visual inspection is then carried out using a light microscope to identify any colon cancer cells present. Unfortunately, this diagnostic is usually done at a stage when the disease is quite advanced and had remained unconfirmed. Late diagnosis often represents a lower success rate for a positive outcome following treatment in this particular form of cancer. Moreover, this method provides no information about the molecular biology of the tumour and its aetiology. Earlier diagnosis is much more desirable while a spectroscopic technique might also provide useful information as to cause.

In spectroscopic histopathology (SHP), the team records spatially resolved vibration spectra of a tissue using either an infrared or a Raman microscope. The spectra reflect the condition of all proteins in a tissue at the site measured so they can see known changes that occur only when cells are cancerous. Ten million spectroscopic scans are recorded to obtain a single tissue image and then software running on a standard personal computer is applied to compare the features of this array of spectra with a reference database - built with software created by Andrea Tannapfel and Axel Mosig and colleagues - of spectra from definitive tumour samples. This provides the team with a spatially resolved annotated image of the colon tissue section.

SHP has been established at the RUB Department of Biophysics to discern molecular changes that have occurred in cancerous tissues directly; specifically it can see changes in proteins. SHP might even be able to detect changes that occur earlier in the growth of a tumour when early therapeutic intervention has a higher likely success rate. The team points out that since their approach requires no fluorescent dye to stain samples and indeed does not require a biopsy at all it can be used on live tissue using a fibre-optic probe. "In the future, we intend to work together with clinical partners and apply spectral histopathology to patients directly via endoscopes," explains Gerwert.

The team has demonstrated proof of principle of SHP and compared its sensitivity and specificity against classical immunohistochemical methods, in which tumours are identified with the aid of fluorescent labels. "The results match perfectly," says Gerwert. "It demonstrates impressively that spectral histopathology is capable of determining changes in tissue composition with high sensitivity and in an automated fashion," he adds. Sensitivity and specificity of SHP are greater than 95 percent. The use of Raman imaging, rather than infrared, boosts the spatial resolution significantly, although it takes longer to obtain the requisite spectra. "Both methods complement each other excellently," comments Gerwert. "Infrared spectroscopy gives you a rapid overview of the entire tissue section. We can then analyse suspicious regions in more detail by applying Raman imaging." Raman analysis, for example, reveals altered nuclei which are characteristic of tumours.

Related Links

J Biophotonics 2013, online: "Immunohistochemistry, histopathology and infrared spectral histopathology of colon cancer tissue sections"

Analyst 2013, online: "Spectral Histopathology of colon cancer tissue sections by Raman imaging with 532 nm excitation provides label free annotation of lymphocytes, erythrocytes and proliferating nuclei of cancer cells"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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