Tycel Phillips, MD, University of Michigan, Ann Arbor, MI, discusses the Phase II CITADEL-204 study (NCT03144674) evaluating the safety and efficacy of a potent, highly selective phosphatidylinositol 3 kinase (PI3K) δ inhibitor, parsaclisib, in patients with relapsed/refractory (R/R) marginal zone lymphoma (MZL). In a patient cohort naïve to Bruton’s tyrosine kinase (BTK) inhibitors, an overall response rate (ORR) of 57.6% was observed. The response rates were comparable across MZL subtypes including nodal, extranodal or splenic MZL. The interim safety data suggests that parsaclisib is generally well tolerated, with expected toxicities such as neutropenia and diarrhea. This interview took place during the 62nd American Society of Hematology (ASH) Annual Meeting and Exposition, 2020.