Patients with relapsed or refractory B-cell non-Hodgkin lymphomas who are not candidates for hematopoietic stem cell transplant have a generally poor prognosis and few treatment options, but an experimental combination of the antibody-drug conjugate naratuximab with rituximab showed promising efficacy and acceptable safety in these patients in a phase 2 trial.
Among patients with relapsed/refractory diffuse large B-cell lymphoma (DLBCL) the combination was associated with a 44.7% overall response rate, including 31.6% complete responses, and two-thirds of patients had responses lasting more than 12 months, reported Moshe Yair Levy, MD, from Texas Oncology–Baylor Charles A Sammons Cancer Center in Dallas.
“This is, in my viewpoint, very exciting therapy,” he said in a question-and-answer session following his presentation of the data in a late-breaking abstract session during the European Hematology Association annual congress. (Abstract LB1903).
Naratuximab emtansine is an investigational antibody-drug conjugate (ADC) consisting of a humanized monoclonal antibody against CD37, a surface marker on B lymphocytes that is highly expressed in non-Hodgkin lymphoma (NHL), conjugated to a cytotoxic derivative of maitansine.
CD37 is also an internalizable cell-surface antigen, making it an attractive candidate for an ADC approach.
In a phase 1 trial, naratuximab monotherapy showed a good safety profile and a 22% overall response rate, Dr. Levy noted.
“What they found is that, if you coadminister this ADC with rituximab, you’re actually going to get more internalization of the CD37 monoclonal, therefore more payload delivered to your target cells,” he said.
He reported results of a multicenter, adaptive phase 2 study of the combination in patients with DLBCL and other relapsed/refractory NHL.
DLBCL and others
The trial was divided into two parts, with the first consisting of a safety run-in phase with expansion in patients with confirmed diagnoses of relapsed/refractory NHL, including DLBCL, follicular lymphoma, mantle cell lymphoma, and marginal zone lymphoma.
Patients with double- or triple-hit disease (with translocations in MYC plus either BCL2 and/or BCL6), bulky disease, or transformed lymphoma were eligible.
The second part consisted of two cohorts of patients with DLBCL treated with naratuximab and rituximab either weekly or every 3 weeks.
All patients in the study had received one to six prior lines of therapy, and had Eastern Cooperative Oncology Group performance status of 0-2. Patients with CNS lymphomas or prior anti-CD37 targeting therapy were excluded.
The safety population included 50 patients with DLBCL assigned to therapy every 3 weeks, 30 assigned to weekly therapy, and 20 patients with other NHL.
DLBCL efficacy
A total of 76 patients with DLBCL were evaluable for efficacy.
The ORR was 44% for patients in both the weekly and every 3 week cohorts, with 31.6% having complete responses.
Among 61 patients with nonbulky disease (longest diameter 7.5 cm or less), the ORR was 50.8%, and among 28 patients who had three or more prior lines of therapy the ORR was 46.4%, with 32.1% having a complete response.
Among responders followed for a median of 15 months, the median duration of response was not reached, and 66% had responses lasting beyond 12 months.
In the weekly dosing DLBCL cohort, 53.3% of patients discontinued treatment of both study drugs because of disease progression, as did 58% of those in the every 3 week cohort, and 30% of patients with other lymphomas. Only eight patients discontinued the combination because of treatment-emergent adverse events. Six patients had treatment-emergent adverse events leading to naratuximab dose reduction.
The most common grade 3 or 4 adverse events were neutropenia, leukopenia, lymphopenia and thrombocytopenias. Dr. Levy commented that the use of granulocyte colony-stimulating factor, which was not mandatory in the study, would likely have lowered the incidence of cytopenias.
There were 10 deaths during the study, 2 of which were considered to be treatment related, occurring in 1 patient each in the DLBCL dosing cohorts; 1 of the patients died from pneumonitis, and the other from left ventricular heart failure.
Other patients deaths were attributed to non–treatment-related cardiac arrest, acute renal failure, exacerbation of chronic heart failure, respiratory failure, multiorgan failure, lung infection, or colon adenocarcinoma.