Glioma—a type of brain cancer that infiltrates surrounding tissue—is hard to distinguish visually and texturally from the surrounding healthy tissue. Surgeons need to remove as much of the cancer as possible while minimizing removal of healthy tissue. A team led by R. Graham Cooks of Purdue University and pathologist Eyas M. Hattab and neurosurgeon Aaron A. Cohen-Gadol of Indiana University School of Medicine have now used desorption electrospray ionization mass spectrometry in the operating room to assess tumor border during surgery to remove glioma (Proc. Natl. Acad. Sci. USA 2017, DOI: 10.1073/pnas.1706459114). The researchers obtained mass spectra of biopsied tissue smears in the operating room within three minutes, which is fast enough to be useful for making decisions during surgery. By using mass spec signals associated with membrane-derived lipids and N-acetylaspartate, the researchers were able to distinguish among glioma, white matter, and gray matter in the brain. In addition, they were able to detect a previously known glioma prognostic marker and determine the percentage of tumor cells in the biopsies. They followed the mass spectrometry determinations with conventional histopathological evaluations.