Blinatumomab for Patients with Richter's Syndrome: A Multicenter Phase 2 Trial from the Filo Group

Background

Richter syndrome (RS) refers to the onset of aggressive lymphoma, mostly diffuse large B cell lymphoma (DLBCL), in patients with chronic lymphocytic leukemia (CLL). The outcome of RS patients is usually very poor with both low response rates to chemoimmunotherapy and short survival. While BCR and BCL2 inhibitors have transformed the management of CLL patients, these drugs do not prevent the onset of RS. Modulating anti-tumor immunity has recently been suggested as a promising approach in RS (Ding, 2017).

Blinatumomab is a bi-specific T-cell engaging antibody construct that transiently links CD3-positive T cells to CD19-positive B-cells, inducing T-cell activation and subsequent lysis of tumor cells. It has been approved for the treatment of patients with relapsed or refractory B-ALL and has also been evaluated in the setting of persisting minimal residual disease. Recently, blinatumomab (stepwise dosing 9-28-112 μg/d) has been evaluated in patients with relapsed or refractory DLBCL and demonstrated promising results (ORR 43%) with acceptable safety (Viardot, 2016).

We hypothesized that blinatumomab would improve response in RS patients failing to achieve CR after initial debulking with R-CHOP.

Methods

We report here the first results of a phase 2 multicenter study investigating the efficacy and safety of blinatumomab after R-CHOP debulking therapy for patients with untreated RS of DLBCL histology (NCT03931642). The patients with persisting (PR, SD) or progressive disease (PD) after 2 cycles of R-CHOP were eligible to receive an 8-week course of blinatumomab induction. Blinatumomab was administered at a stepwise dose of 9 μg/d in the first week, 28 μg/d in the second week, and 112 μg/d thereafter. The primary endpoint was CR rate according to the revised Lugano criteria after the 8-week induction course of blinatumomab. An additional 4-week consolidation cycle was optional. Allo-HSCT was further allowed for eligible patients.

Results

A total of 34 patients out of 41 has already been enrolled in the trial to date. Median age was 66 years (range, 38-82) and sex ratio M/F was 23/12. CLL features at baseline were as follows: 57% had 17p deletion and 67% TP53 mutations. Sixty-five percent had complex karyotype and 79% unmutated IGHV status. Median number of prior therapeutic lines for CLL was 2 (range, 0-7): 19 (54%) patients previously received chemo-immunotherapy, 23 (66%) patients were exposed to ibrutinib and 11 (31%) to venetoclax.

As of the data cut-off of June 1st, 2021, the blinatumomab induction course has been completed for 18 patients. Ten patients did not receive blinatumomab for the following reasons: 7 patients achieved CR after R-CHOP, 2 patients died because of febrile neutropenia after R-CHOP and 1 patient presented severe pneumonia after R-CHOP. Three patients are still on R-CHOP and 3 others on blinatumomab to date.

Regarding toxicity during blinatumomab, data are available for the 18 patients having completed the blinatumomab induction to date. All patients had at least one grade 1 adverse event (AE), 10 had grade ≥3 AE. The most common AE (> 1 case), regardless of relationship to blinatumomab, were fever (4 patients), CRS (2 patients), sepsis (2 patients), vein thrombosis (2 patients), anemia (4 patients), neutropenia (3 patients), lymphopenia (5 patients), thrombocytopenia (3 patients) and hyperglycemia (5 patients). In terms of neurologic events, 5 (28%) experienced neurotoxicity (all recovered) including grade 3 encephalopathy, grade 4 confusion, grade 3 anxiety, grade 1 myoclonus, grade 2 ataxia, grade 1 sleep disorder and grade 1 ICANS (each in 1 pt). Blinatumomab was temporarly stopped in 3 patients and permanently in 2.

In terms of efficacy, after R-CHOP debulking therapy (n=31 evaluable patients), 7 patients achieved CR, 6 patients were in PR, 7 patients were stable and 11 patients were progressive. At evaluation after the blinatumomab induction (n=18 evaluable patients), 4 (22.2%) patients achieved CR, 4 (22.2%) patients PR, 2 (11.1%) patients were stable and the remaining 8 (44.5%) were progressive. Considering the whole strategy (including R-CHOP debulking) (n=28), 15 (54%) patients achieved overall response including 11 (39%) CR.

Conclusions

Our preliminary data suggest that blinatumomab suggests encouraging anti-tumor activity and acceptable toxicity in patients with RS.