Risk stratification for smoldering multiple myeloma. The model incorporates three risk factors: abnormal FLC ratio, bone marrow plasma cells ⩾10% and serum M protein ⩾3 g/dl. Patients with 1, 2 or 3 risk factors had 5-year progression rates of 25, 51 and 76%, respectively. Corresponding median times to progression are 10, 5.1 and 1.9 years, respectively.