Real-Time Molecular Diagnosis of Tumors Using Atmospheric Pressure Infrared Matrix-Assisted Laser Desorption-Ionization Mass Spectrometry

International audience; Tissue diagnosis is critical in the clinical management of cancer patients. Mass Spectrometry (MS) has long been of interest for discriminating cells using tissue sections of patient biopsies. However, the main challenge arises in the context of intraoperative tissue analyses, where the MS instrument must operate within a surgical environment. To date, only the Intelligent Knife (iKnife) system allowed real-time monitoring during surgery by collecting aerosol released during tissue excision with an electric scalpel or bipolar forceps [1]. Recently we have demonstrated that in vivo real-time analyses can be less invasive using laser ablation. In our prototype, a fibered IR Optical Parametric Oscillator (OPO) is tuned at 2.94 µm to excite the most intense vibrational band (O-H stretching mode) of water molecules found abundantly in all biological tissues. Water acts as a natural endogenous Matrix-Assisted Laser Desorption-Ionization (MALDI) matrix leading to the production of ions that can be transported over a few meters to a MS instrument for analysis without requiring further post-ionization handling. The molecular patterns (metabolites, lipids and proteins) thus retrieved are specific to cell phenotypes and benign versus cancer regions can easily be differentiated [2]. We present the first assessment of our prototype in a veterinary surgery room [3]. For this purpose, a series of benchmark studies have been initiated with the aim of building up an extensive databank able to relate distinct molecular profiles to a specific type of pathology, namely the dog sarcoma. These studies are accompanied by the development of a real-time query interface. Classification models based on tumor grade (cancer/normal/necrotic) and cancer subtype developed in this work showed a minimum of ~98% correct classification when put to use. The system demonstrated clear-cut margin detection capabilities that have been validated in correlation with histology. Finally, this instrument enables real-time diagnostics by the immediate interrogation of classification models established ahead of time.