ABSTRACT
INTRODUCTION: Between 2014 and 2018 The United States Food and Drug Administration granted approvals for three small molecule inhibitors of phosphoinositide 3-kinases (PI3Ks) as monotherapy for follicular lymphoma relapsed after at least 2 prior therapies. Idelalisib, copanlisib, and duvelisib each showed similar overall response rate and progression-free survival efficacy along with significant toxicity in separate phase II single-arm studies. Umbralisib, as the 4th iteration in this PI3K-inhibitor class for relapsed/refractory indolent B-cell lymphoma (iB-NHL), appears comparably active but may have improved tolerability. AREAS COVERED: We review the use and limitations of PI3K-inhibitors for iB-NHL and discuss the development of and clinical results for umbralisib. Efficacy data are contextualized alongside other PI3K-inihibitors within the limitations of published single-arm studies. We compare and contrast available safety data, covering the off-target inhibition by umbralisib of casein kinase 1ε that is thought to contribute to a more favorable immune-mediated toxicity profile. EXPERT OPINION: Though a late-comer to the PI3K-inihibitor party in iB-NHL, umbralisib may carve out an important role in treatment algorithms. Umbralisib's apparently superior safety needs to be confirmed in real-world and, ideally, comparative studies but stands to make it an attractive option in patients who are frail and/or seek treatments more compatible with remote management.
