Alisertib in combination with romidepsin is synergistic in TCL but not in BCL. The IC10–20 of romidepsin (R) was used in combination with 50, 100, 1,000 nmol/L (IC10–30) of alisertib (A) to evaluate drug:drug interactions for up to 72 hours of treatment. A and B, following 72 hours of simultaneous drug exposure, synergy was not observed in a representative panel of BCL cell lines. EOB values were in the range of −20.03 to 5.83, signifying an antagonistic drug:drug interaction. C and D, following 72 hours of simultaneous drug exposure, synergy was observed in a panel of TCL cell lines with EOB values ranging from −9.05 to 21.01.