Phase I Study of Rituximab, Lenalidomide, and Ibrutinib in Previously Untreated Follicular Lymphoma (Alliance 051103)

Background

Chemoimmunotherapy for advanced stage follicular lymphoma (FL) is associated with acute and long-term toxicity; targeted therapy may improve efficacy and tolerability in this incurable, multiply-relapsing disease. The Alliance for Clinical Trials in Oncology previously demonstrated the efficacy of lenalidomide (20 mg D1-21/28) and rituximab (R²) in untreated FL patients (pts): ORR 93%, CR 72%, 2-yr PFS 89% (Martin P, et al. ASCO 2014), which supported the ongoing phase III RELEVANCE study of R² vs. R-chemo. Attempts at improving R² include incorporation of other agents. The BTK inhibitor, ibrutinib (I), demonstrated an ORR of 30-55% (Bartlett N et al. ASH 2014, Fowler N et al. ASH 2012) in relapsed/refractory FL. Based on these data, the Alliance designed a multicenter phase I study of this triplet as a front-line regimen for FL.

Methods

Pts with previously untreated, grade 1-3a FL, Stage III, IV, or bulky stage II disease, performance status < 2, and adequate organ function were eligible. Pts received R 375 mg/m² on Cycle 1 D 1, 8, 15, 22 and at week 13, 21, 29, and 37 for 8 doses, lenalidomide (L) as per cohort dose on D1-21/28 for 18 months, and I as per cohort dose on D1-28/28 until progression or unacceptable toxicity. Dose escalation used a 3+3 design from a starting level of L 15 mg and I 420 mg (DL0) to DL2 (L 20 mg, I 560 mg). Pts received allopurinol 300 mg daily for tumor lysis prophylaxis. The primary endpoint was the recommended phase II doses (RP2D) of L and I for combination with R in previously untreated FL. The secondary endpoints were toxicity, pharmacokinetics, and preliminary efficacy. Once the MTD was determined, there was a 10-patient expansion cohort. Due to the known incidence of rash with L, grade 3 rash that resolved to < grade 2 in 10 days with supportive care including systemic corticosteroids was prospectively not included as a DLT. The incidence of grade 3/4 rash with R² and ibrutinib are 8% and 3%, respectively.

Results

Twenty-two pts were enrolled between June 2013 - May 2015: DL0 (n=3), DL1 (n=3), DL2 (n=16). Median age was 53.5 years (range 36-81); 68% were male, 73% had grade 1/2 disease, 77% had Stage IV disease. By FLIPI, 18% were low risk, 55% were intermediate risk, and 27% were high risk. There were no dose limiting toxicities reported at any dose level. Dose level 2 (L 20 mg, I 560 mg) was found to be the RP2D.

Grade 3/4 hematologic toxicities included neutropenia 18.2%, thrombocytopenia 4.5%, and anemia 4.5%. There were no grade 4 non-hematologic toxicities. Rash occurred in 73% of pts (grade 1/2: 41%, grade 3: 32%), typically during C1-4. Grade 3 rash was noted at every dose level: DL 0 (n=1), DL1 (n=1), DL2 (n=6); 4 pts were on allopurinol at time of grade 3 rash. Several pts successfully continued therapy with discontinuation of allopurinol and/or reduction in treatment dose. Other notable grade 3 non-hematologic adverse events included atrial flutter/chest pain (n=1), diarrhea (n=1), and febrile neutropenia (n=1). Other grade 1/2 non-hematologic adverse events included diarrhea 41%, fatigue 36%, nausea 27%, and AST/ALT elevation 18%. Elevenpts required dose reduction, 8 due to rash.

The ORR for all pts was 91% (CR/CRu 63%). Seven pts with bone marrow involvement did not undergo a confirmatory bone marrow biopsy to rule out residual disease after achieving a negative PET/CT. The ORR at DL2 was 94% (CR/CRu 63%). Median time to response was 5.6 months (range 1.9-18.4), and median time on treatment was 12.6 months (range 3.4-23.4). At the time of this report, 3 pts have progressed (DL1 (n=1), DL 2 (n=2)). At median follow-up time of 12 months, the 12-month PFS for all pts was 84% (95% CI: 57-94%). The 12-month PFS for the DL2 cohort was 86% (95% CI: 54% - 96%). Twelve pts discontinued therapy: progression (n=2), adverse events [grade 3 rash (n=2), grade 3 atrial flutter (n=1), grade 3 diarrhea (n=1)], patient decision (n=3), new diagnosis of carcinoma (n=2), depression (n=1).

Conclusion

Although protocol-defined DLT was not observed, the combination of rituximab, lenalidomide, and ibrutinib in previously untreated follicular lymphoma was associated with a significant incidence of rash, which may have been related to allopurinol, the individual study drugs, or drug interactions. Preliminary ORR data of the regimen were comparable to prior reports of the R² regimen in this population. Efficacy of the combination, including CR rate, may be affected by the reduction in dose intensity.