Abstract: The present invention refers to a process for classifying tumor samples of unknown and/or uncertain primary origin, specifically including the steps of obtaining patterns of biological activity modulation of tumor of unknown and/or uncertain primary origin and comparing them to an specific and unique group of biomarkers which determine the profiles of biological activity modulation of known origin tumors. The present invention belongs to the molecular biology and genetics field.

Abstract: The present invention relates to the determination of the presence of methylmalonic acid in biologic samples including the steps of methylmalonic extraction from the sample; derivatization of methylmalonic acid and use of mass spectrometry with negative mode atmospheric pressure chemical ionization to determine the presence of methymalonic acid through the formation of an ion of mass to charge ratio (m/z) 477. An additional objective of the present invention concerns diagnosis kits for determination of presence and quantification of methylmalonic acid based on the method mentioned before.