Unlike bone marrow bio psies, liquid bio psies represent a gentler, more accessible, less painful,repeatable and more comprehensive approach to get bio logically relevant information about the entire tumor but also about treatment response and level of minimal residual disease. This is all possible since peripheral blood contains not only circulating tumor cells but also many circulating molecules of nucleic acids (microRNA, cell-free DNA, long non-coding RNA etc.).Multiple myeloma is a genetically heterogeneous disease characterized by multifocal tumor deposits in the bone marrow but also focal lesions elsewhere. Single-site bio psy of the bone marrow creates a sampling bias that provides a limited molecular profile as the bio psy cannot capture all subclones. Moreover, during disease progression and treatment, molecular profile is changed and subclones of multiple myeloma cells resistant to treatment are formed. Likewise,various clones found in extramedullary sites that are not present in the bone marrow respond differently to treatment directly influencing survival of patients. Thus, liquid bio psies seem to be a relevant and necessary next step for diseases such as multiple myeloma.