Abstract: The present invention responds to the need to provide an endogenous miRNA for quantifying the amount of one or more targets miRNA in exosomes using normalization, that that does not vary within the different tumor types and within the different chemotherapeutic treatments. This is essential to be able to perform robust analysis of the expression of exosomal miRNAs in these pathologies. So far, other types of endogenous controls have been used that are not strictly exosomal, thus reducing their reliability as normalizers. Therefore, for the first time, an endogenous control specific for the exosomal compartment would be available.