Detection of human brain tumor infiltration with quantitative stimulated Raman scattering microscopy

Quantitative SRS microscopy can detect human brain tumor infiltration with high sensitivity and specificity, even in tissues appearing grossly normal. Image-based classifier calls out cancer cells Ji and colleagues used a microscopy technique called stimulated Raman scattering, or SRS, to image cancer cells in human brain tissue. SRS produces different signals for proteins and lipids, which can then be assigned a color (blue and green, respectively), allowing the authors to differentiate brain cortex from tumor from white matter. Biopsies from adult and pediatric patients with glioblastoma revealed not only distinctive features with SRS microscopy but also the presence of infiltrating cells in tissues that appeared otherwise normal with traditional staining. Such infiltrating cells are important to catch early because leaving them behind after surgery nearly always leads to cancer recurrence. To make this SRS microscopy approach amenable to routine use in neuropathology, the authors also created an objective classifier that integrated different image characteristics, such as the protein/lipid ratio, axonal density, and degree of cellularity, into one output, on a scale of 0 to 1, that would alert the pathologist to tumor infiltration. The classifier was built using more than 1400 images from patients with glioblastoma and epilepsy, and could distinguish between tumor-infiltrated and nontumor regions with >99% accuracy, regardless of tumor grade or histologic subtype. This label-free imaging technology could therefore be used to complement existing neurosurgical workflows, allowing for rapid and objective characterization of brain tissues and, in turn, clinical decision-making. Differentiating tumor from normal brain is a major barrier to achieving optimal outcome in brain tumor surgery. New imaging techniques for visualizing tumor margins during surgery are needed to improve surgical results. We recently demonstrated the ability of stimulated Raman scattering (SRS) microscopy, a nondestructive, label-free optical method, to reveal glioma infiltration in animal models. We show that SRS reveals human brain tumor infiltration in fresh, unprocessed surgical specimens from 22 neurosurgical patients. SRS detects tumor infiltration in near-perfect agreement with standard hematoxylin and eosin light microscopy (κ = 0.86). The unique chemical contrast specific to SRS microscopy enables tumor detection by revealing quantifiable alterations in tissue cellularity, axonal density, and protein/lipid ratio in tumor-infiltrated tissues. To ensure that SRS microscopic data can be easily used in brain tumor surgery, without the need for expert interpretation, we created a classifier based on cellularity, axonal density, and protein/lipid ratio in SRS images capable of detecting tumor infiltration with 97.5% sensitivity and 98.5% specificity. Quantitative SRS microscopy detects the spread of tumor cells, even in brain tissue surrounding a tumor that appears grossly normal. By accurately revealing tumor infiltration, quantitative SRS microscopy holds potential for improving the accuracy of brain tumor surgery.