S208: EFFICACY AND SAFETY OF ZANDELISIB ADMINISTERED BY INTERMITTENT DOSING (ID) IN PATIENTS WITH RELAPSED OR REFRACTORY (R/R) FOLLICULAR LYMPHOMA: PRIMARY ANALYSIS OF THE GLOBAL PHASE 2 STUDY TIDAL

Abstract

Background: Zandelisib, a PI3Kδ inhibitor with high target-binding affinity, is administered by intermittent dosing (ID) on days 1 to 7 of 28-day cycles to potentially enable regulatory T-cell repopulation and lower the risk of immune-related adverse events (irAEs) associated with continuous PI3Kδ inhibition. In a phase 1b study in 37 patients (pts) with R/R FL, zandelisib administered daily for two 28-day cycles for tumor debulking then on ID achieved an overall response rate (ORR) of 87% (78% as single agent and 95% with rituximab), a median duration of response (DOR) not reached at median follow-up of 16.9 months, and a low rate (<10%) of grade 3 irAEs (Pagel et al. ICML 2021; #113). Aims: We conducted the TIDAL study (NCT03768505) to further evaluate in a global trial the efficacy and safety of zandelisib in larger group of pts with R/R FL and marginal zone lymphoma (MZL). The MZL cohort is still enrolling and not reported here. Methods: Eligible pts ≥18 years with FL Grade I-IIIA, ECOG performance status 0-1, progressive disease after ≥2 prior therapies including an anti-CD20 antibody and chemotherapy, and no prior PI3Kδ inhibitor, provided consent and then received zandelisib 60 mg daily for two 28-day cycles then on ID. Another study arm evaluating zandelisib 60 mg daily continuously was closed to enrollment early and is not reported here. The planned sample size in FL was 120 pts on ID, with the primary efficacy population (PEP) pre-defined as the first 91 pts treated and the safety population consisting of all FL pts treated. The primary efficacy endpoint was ORR as assessed by independent review using the Lugano criteria and analyzed 6 months after completing enrollment in the PEP. Results: 121 FL pts were enrolled. In the PEP (N=91 pts), the median number of prior therapies was 3 (range 2-8), 21 pts (23%) have received prior stem cell transplant, 42 pts (46%) were refractory to last therapy, 31 pts (34%) had tumors ≥5 cm, and 51 pts (56%) were POD24. The ORR was 70.3% (N=64) (95% CI 59.8-79.5%), with 32 pts (35.2%) achieving a complete response (CR). Responses occurred early, with 85.5% (N=56) achieved in the first 2 cycles of therapy and 75% of CRs (N=24) achieved the first 4 cycles. The data are still immature to estimate accurately the DOR. With a median follow-up of 9.4 months (range 0.8-24) in the safety population of 121 pts, 12 pts (9.9%) discontinued therapy due to any drug-related AE. Grade 3 AEs of special interest (AESI) were diarrhea in 6 pts (5%), colitis in 2 (1.7%), cutaneous rash in 4 (3.3%), stomatitis in 3 (2.5%), and 1 (0.8%) each for AST and ALT elevation, and non-infectious pneumonitis. Grade 3 AESIs primarily (15 of 18, 83%) occurred in cycles 1-3, during daily dosing, with only 3 cases reported on ID in Cycles ≥4. Summary/Conclusion: Zandelisib on ID achieved high ORR (70.3%) and CR rate (35.2%) in heavily pretreated R/R FL pts, and was associated with a low rate (<10%) of grade 3 AESI and discontinuations due to AEs, results comparable to the Phase 1b study. Longer follow-up is needed to estimate median DOR. This profile supports evaluation of zandelisib as a single agent and in combination regimens in various B-cell malignancies, both in R/R disease and in earlier lines of therapy. Zandelisib plus rituximab vs chemoimmunotherapy is being evaluated in the phase 3 study COASTAL in R/R FL and MZL (NCT04745832).