Brain tumours show a low prevalence as compared to other cancer pathologies. Their impact, both in individual and social terms, far outweighs such low prevalence. Their anatomical specificity also makes them difficult to explore and treat. The use of biopsies is limited to extreme cases due to the risks involved in the surgical procedure, and non-invasive measurements are the standard for diagnostic exploration. The usual measurement techniques come in the modalities of imaging and spectroscopy. In this chapter, the authors analyze magnetic resonance spectroscopy (MRS) data from an international database and illustrate the importance of data preprocessing prior to diagnostic classification.