HDAC9 and lymphoma: In summary, evidence of PLK1 activity in pre-clinical DLBCL and other NHL models [21, 45], early signals of activity of volasertib in lymphoid malignancies [23], and the present findings demonstrating potentiation of volasertib anti-lymphoma efficacy by HDACIs support the development of a PLK1/HDAC inhibitor regimen in NHL.