Expression levels of p21 and p27in different stages of plasma cell disorders. Semiquantitative assessment of plasma cells positive for p21 (a) and p27 (b) is shown in healthy controls, MGUS, SMM, MM, and EMM patients. Significant differences in expression levels between cohorts are indicated by their respective p-values with * p-value < 0.05, ** < 0.01, *** < 0.001.