Abstract: Exosomes can be used for detecting biomarkers for diagnostic, therapy-related or prognostic methods to identify phenotypes, such as a condition or disease, for example, the stage or progression of a disease. Cell-of-origin exosomes can be used in profiling of physiological states or determining phenotypes. Biomarkers or markers from cell-of-origin specific exosomes can be used to determine treatment regimens for diseases, conditions, disease stages, and stages of a condition, and can also be used to determine treatment efficacy. Markers from cell-of-origin specific exosomes can also be used to identify conditions of diseases of unknown origin.