Multiple myeloma (MM) is the second most common hematological malignancy of the elderly. It is caused by the proliferation of malignant plasma cells that influence physiological hematopoiesis, bone structure, and the immune system the most. As the population ages, age-specific diseases become more and more important. There is a subtype of MM called extramedullary disease, which is caused by the migration of subclones of plasma cells that lose their dependence on the bone marrow microenvironment. This is connected to a worse prognosis for the patients. The extramedullary disease needs to be diagnosed by specific imaging methods (PET/CT, MRI) that may not be available in all centers or may take too much time. Liquid biopsies, biopsies from peripheral blood, are faster, patient-friendly and show real promise. We propose to use a combination of MALDI-TOF mass spectrometry with short RNA sequencing to detect extramedullary disease and correlate these results with PET/CT imaging.