PI3Kδ Inhibitor Parsaclisib in Japanese Patients With Relapsed or Refractory Follicular Lymphoma

Follicular lymphoma (FL) is the second most common subtype of non-Hodgkin lymphoma (NHL) in Japan, the United States, and Western Europe. Parsaclisib is a potent, selective next-generation PI3Kδ inhibitor that has demonstrated clinical efficacy and tolerability in phase II studies of patients with relapsed or refractory (R/R) B-cell NHL, including FL. We report results from CITADEL-213 (NCT04434937), a phase II study evaluating the efficacy and safety of parsaclisib in Japanese patients with R/R FL. Eligible patients were aged ≥ 18 years with histologically confirmed R/R FL (grade 1, 2, or 3a), had received two or more prior systemic therapies, and were ineligible for hematopoietic stem cell transplantation. Patients received parsaclisib 20 mg once daily for 8 weeks, followed by parsaclisib 2.5 mg once daily thereafter. The primary endpoint was the objective response rate (ORR). At the data cut-off (February 16, 2023), 42 patients had received treatment with parsaclisib, of whom 41 were evaluable for change in target tumor size. Median (range) age at baseline was 66.5 (52-87) years. ORR (95% confidence interval [CI]) was 88.1% (74.4-96.0), with 10 patients (23.8%) experiencing a complete response and 27 patients (64.3%) experiencing a partial response. Median (95% CI) duration of response was not reached (8.0 months-not estimable). The most common treatment-emergent adverse events (TEAEs) were diarrhea (28.6%; grade ≥ 3, 7.1%) and stomatitis (23.8%; grade ≥ 3, 11.9%); TEAEs led to parsaclisib discontinuation in five patients (11.9%). There were no fatal TEAEs. In conclusion, parsaclisib monotherapy demonstrated durable responses with a manageable safety profile in Japanese patients with R/R FL. Trial Registration: ClinicalTrials.gov, NCT04434937.