Temsirolimus in Combination with Bendamustine and Rituximab for the Treatment of Relapsed Mantle Cell and Follicular Lymphoma: Report on an Ongoing Phase I/II Trial

Background: mTOR inhibition has been shown to be effective in various subtypes of malignant lymphomas. In relapsed MCL a phase III trial could prove superiority of Temsirolimus to standard options. Furthermore, in patients with follicular and diffuse large B-cell lymphoma, promising response rates could be observed (Smith et al, JCO 2010). Whereas combination to single agent Rituximab (R) improved efficacy (Ansell et al, Lancet Oncology 2011), there is limited information of the feasibility and efficacy in combination with chemotherapy. Bendamustine (B) has been shown to be effective in various lymphoma entities and has a beneficial side effect profile (Rummel et al, JCO, 2005). In the phase I of this trial, we have established that 50mg of Temsirolimus given 3 times weekly in a four week cycle could be safely added to BR (Hess, Leukemia, 2015). Here we report for the first time combined results of phase I and II of this trial.

Methods: this is a multicenter, national, prospective trial. Inclusion criteria: patients were eligible if they had histologically proven FL or MCL, 1-3 prior treatment lines, no curative option available, no refractoriness to Bendamustine, measurable disease, ECOG < 3, sufficient bone marrow reserve, no severe concomitant diseases and given informed consent. Treatment consisted of Bendamustine 90mg/m² day 1-2, Rituximab 375mg/m² day 1 and Temsirolimus 50 mg day 2, 8, 15 of a 28d cycle. A total of 4 cycles was planned with interim staging after 2 cycles.

Results: Overall 34 patients (pts) have been included until now (15 pts phase I, 19 pts phase II). Concerning clinical characteristics, median age was 71 years, with 25 MCL and 9FL, and a median number of 2 pretreatments (1-3). Overall the treatment was well tolerated, and toxicity was predominantly hematologic. In 118 evaluable cycles of chemotherapy the following hematologic grade 3 / 4 toxicities were noted: leukopenia (11 pts, 32%), neutropenia (8 pts, 24%), and thrombocytopenia (7 pts, 21%). Non-hematologic grade 3 / 4 observed in at least two patients were angioedema and decrease in blood potassium, infection, metabolic (4 events). AE's of special interest: pulmonary: rate of cough (4; 12%) and pneumonitis (1; 3%); gastrointestinal: diarrhea (6; 18%), nausea (13, 38%); general: fatigue (16; 47%), mucositis (13, 38%); bleeding: epistaxis (4; 12%), which all were predominantly grade 1 or 2. Response: currently, best responses were 8 CR (31%), 16 PR (62%) and 2 SD (8%) in 26 patients evaluable so far. Updated results will be presented at the meeting. Overall responses were 94% in MCL (7 CR, 10 PR, 1 SD) and 88% in FL (1 CR, 6 PR, 1 SD). After a median follow up of 13 months (mean: 21 months) median PFS is 18.6 months for the entire cohort, with 22 months for MCL and not reached in FL.

Summary: In this ongoing phase II trial 50mg Temsirolimus (day 1,8,15) in combination with Bendamustine and Rituximab was well tolerated and feasible. A moderate dose of Temsirolimus to standard chemotherapy might be the optimal way to achieve the maximum efficacy with mTOR inhibitors; in fact excellent response rates suggest an additive effect of mTOR inhibition to BR. Even after the BTK inhibitor Ibrutinib has entered the clinical arena of MCL, this combined treatment represents a valuable additional option especially for patients with relapsed MCL