Frequencies of immunoglobulin (Ig) rearrangement in the bone marrow of MPN patients receiving conventional therapy (n = 44) or JAK inhibition (n = 54). In this latter cohort, 3/54 (5.6%) patients developed an aggressive B-cell lymphoma, and all of them had in their bone marrow a preexisting B-cell clone that was later found to be related to the malignant lymphoma. See Figure 1E in the article by Porpaczy et al that begins on page 694.