Unexpected and Serious Toxicity Observed with Combined Idelalisib, Lenalidomide and Rituximab in Relapsed/Refractory B Cell Lymphomas: Alliance A051201 and A051202

Background: A number of targeted and orally available agents show promising activity in lymphoid malignancies, and a rational strategy is to evaluate combinations for safety and efficacy. Idelalisib (idela) is a highly specific and potent inhibitor of the delta isoform of PI3K, downstream of B-cell receptor signaling and upstream of other survival pathways in lymphoma. Idela has single agent activity in both follicular lymphoma (FL) and mantle cell lymphoma (MCL), with response rates over 50% (N Engl J Med. 2014;370:1008). Idela and rituximab (ritux) have been safely combined in chronic lymphocytic leukemia (N Engl J Med. 2014;370:997) and other indolent lymphomas. Two previous Cancer and Leukemia Group B and Alliance studies demonstrated high levels of clinical activity of lenalidomide (len) and ritux in combination without significant toxicity. In relapsed/refractory FL, len plus ritux had higher overall (ORR) and complete response (CR) rates (75% ORR, 32% CR) versus len alone (49% ORR, 13% CR)(J Clin Oncol. 2012;30(suppl; abstr 8000). In frontline FL, len plus ritux achieved 93% ORR and 72% CR rates (J Clin Oncol 32:5s, 2014 (suppl; abstr 8521). A051201 and A051202 were designed to evaluate the safety and activity of len and ritux, in combination with idela, in pts with relapsed MCL or FL, respectively.

Methods: Both A051201 and A051202 are phase I trials with 3+3 designs and pre-specified dose-limiting toxicities (DLT). Treatment in the two trials was similar but not identical. A051201 started with len 15mg po day (d) 1-21 q28d idela 150mg bid with continuous 28-d cycles, and ritux weekly during cycle 1. A051202 started with len 10mg po d1-21 q28d and idela 150mg po bid with continuous 28-d cycles, and ritux on C1d8, C1d15, C1d22 and C2d1. Both studies included a maintenance component (data not presented). Biweekly conference calls for safety were established. After 3 patients (pts) from A051202 and 1 pt from A051201 developed severe and unexpected DLT, both trials were suspended and modified.

Results: At the time of study suspension, 7 FL pts and 1 MCL pt had been enrolled. Pt characteristics include median age 58.5 years (y) (range, 47-77), 5 male/3 female, and median 1 (range, 1-7) prior treatment; all pts had prior ritux. The MCL pt had an autologous stem cell transplant 3 y prior to enrollment. This pt had a DLT consisting of grade (gr) 4 AST/ALT elevation in the setting of fevers, chills, hypotension at 22 d after treatment initiation. 3 FL pts had DLT consisting of gr 3 lung infection, gr 3 hypotension and rash, and gr 4 sepsis syndrome (culture-negative), respectively. Each of the 3 FL pts with DLT developed fevers and hypotension with or without a rash 11-17 d after treatment initiation and within 24-120 hours of last ritux exposure; 2 pts had pulmonary infiltrates. 3 DLT pts required ICU level support. Other notable toxicities in all 8 pts include gr 1/2 AST/ALT elevation (n=5), gr 3 lymphopenia (n=5), gr 1/2 thrombocytopenia (n=4), grade1/2/3 neutropenia (n=4).

Conclusion: Whereas doublet therapy with len/ritux and idela/ritux has been safely combined in other trials and disease settings, we observed 4 DLTs among the first 8 pts, all concerning for high-level immune activation. Although the mechanism of these toxicities is unknown, the combination of rash, fevers, and hypotension is suggestive of cytokine release syndrome (CRS), which is a known but uncommon IL-6-mediated event seen with ritux, rarely reported after single agent len, and, to date, not observed with idela. Our observation of 4 potential CRS-like reactions among 8 pts suggests an additive and previously undescribed risk of this combination. Based on the severe toxicities noted, both trials have been amended to remove ritux and pursue a phase I safety assessment of idela and len without ritux in pts with relapsed FL or MCL.