The PI3Kδ inhibitor zandelisib on intermittent dosing in relapsed/refractory follicular lymphoma: Results from a global phase 2 study

In this global phase 2 study in patients with relapsed/refractory follicular lymphoma (FL), zandelisib was administered on intermittent dosing to mitigate immune-related adverse events and infections that have been reported with oral PI3Kδ inhibitors administered daily continuously. Eligible patients with measurable disease and progression after at least two prior therapies were administered zandelisib until disease progression or intolerability. The primary efficacy endpoint was objective response rate (ORR) and the key secondary efficacy endpoint was duration of response (DOR). We report on 121 patients with FL administered zandelisib on intermittent dosing after 8 weeks of daily dosing for tumor debulking. The median number of prior therapies was 3 (range, 2–8) and 45% of patients had refractory disease. The ORR was 73% (95% confidence interval [CI], 63.9–80.4), the complete response (CR) rate was 38% (95% CI, 29.3–47.3), and the median DOR was 16.4 months (95% CI, 9.5–not reached). With a median follow-up of 14.3 months (range, 1–30.5), the median progression-free survival was 11.6 months (95% CI, 8.3–not reached). Twenty-one patients (17%) discontinued therapy due to an adverse event. Grade 3–4 class-related toxicities included 6% diarrhea, 5% lung infections, 3% colitis (confirmed by biopsy or imaging), 3% rash, 2% AST elevation, and 1% non-infectious pneumonitis. Zandelisib achieved a high rate of durable responses in heavily pretreated patients with relapsed/refractory FL. The intermittent dosing resulted in a relatively low incidence of severe class-related toxicities, which supports the evaluation of zandelisib as a single agent and in combination with indolent B-cell malignancies.