Parsaclisib in Japanese patients with relapsed or refractory B‐cell lymphoma (CITADEL‐111): A phase Ib study

Parsaclisib, a potent, selective, next‐generation PI3Kδ inhibitor, has shown clinical benefit in patients with relapsed or refractory B‐cell lymphoma. We undertook a phase Ib study (CITADEL‐111) evaluating safety, pharmacokinetics, and efficacy of parsaclisib in Japanese patients with relapsed or refractory B‐cell malignancies. Patients received oral parsaclisib daily for 8 weeks then once weekly (10‐mg dose, n = 3; 20‐mg dose, n = 14). Pharmacokinetic samples were collected on days 1, 8, and 15, and efficacy was monitored according to Lugano criteria. At data cut‐off (August 14, 2020), 6 patients (35.3%) remained on study treatment and 11 (64.7%) discontinued due to progressive disease (9 [52.9%]) or adverse events (2 [11.8%]). Median duration of treatment was 8.3 (range, 0.3–24.4) months. The most commonly reported nonhematologic adverse events were constipation (6 [35.3%]), nausea, and pyrexia (each 4 [23.5%]). Five patients (29.4%) experienced treatment‐emergent new or worsening decreased neutrophils to grade 3 or 4. No treatment‐emergent worsening in aminotransferase elevations to grade 3 or 4 were observed. Ten patients (58.8%) required dose interruption and 5 (29.4%) dose reduction. Body weight–normalized parsaclisib exposure was comparable between Japanese and Western patients. Objective response rate was 100% in follicular lymphoma (9 of 9 patients, including complete response in 2 patients [22.2%]) and marginal zone lymphoma (2 of 2 patients), and 16.7% in diffuse large B‐cell lymphoma (1 of 6 patients). Results observed in Japanese patients with relapsed or refractory follicular or marginal zone lymphoma support further clinical development of parsaclisib in these patient populations.