Treatment options for patients with relapsed or refractory lymphoma and multiple myeloma are limited. CUDC-907 is an oral, first-in-class, small molecule that is designed to inhibit both histone deacetylase (HDAC) and PI3K enzymes, which are members of common oncogenic pathways in haematological malignancies. We aimed to assess overall safety and preliminary activity in this dose-escalation study of CUDC-907 monotherapy in patients with relapsed or refractory lymphoma and multiple myeloma.