Whether CD56 expression by MM cells is associated with virulence is not clearly established; yet, our results show a profound expression of the PCNA on MM cells in the bone marrow, regardless of their CD56 expression and clonality before and after treatment (proteasome inhibition, immunomodulatory imide drugs (IMiDs), and dexamethasone). The gene discussed is PCNA; the disease is Miyoshi myopathy.