SAN DIEGO – Obinutuzumab, a second-generation anti-CD20 antibody touted as the heir apparent to rituximab, offered a progression-free survival (PFS) edge over rituximab when combined with standard chemotherapy in patients with previously untreated advanced follicular lymphoma.
Dr. Robert Marcus
But other clinicians and investigators who
attended the presentation of the GALLIUM data at a plenary session during the American Society of Hematology annual meeting indicated that despite the data, they weren’t ready to make a switch to the newer, costlier antibody.
“I feel that it is not convincing for practice-changing,” said Kanti R. Rai, MD, professor of medicine and molecular medicine at Hofstra University, Hempstead, N.Y.
“Unless we have evidence of a survival advantage in indolent disease, progression-free survivorship is not an adequate reason to jump to another antibody,” he said in an interview.
In GALLIUM, the primary endpoint of investigator-assessed 3-year PFS at a median follow-up of 34.5 months was 80% for patients with follicular lymphoma treated with obinutuzumab and one of three standard chemotherapy regimens, compared with 73.3% for patients treated with rituximab and chemotherapy. This difference translated into a hazard ratio of 0.68 favoring obinutuzumab (P = .0012).
Respective 3-year overall survival rates were similar, however, at 94% and 92.1% (HR, 0.75; P = .21).
Indolent lymphoma trial
The GALLIUM trial is a phase III study comparing obinutuzumab with rituximab when paired with one of three standard chemotherapy regimens for indolent non-Hodgkin lymphomas, including follicular lymphoma and splenic, nodal, or extranodal marginal zone lymphoma. Dr. Marcus presented data on patients with follicular lymphoma only.
The antibodies were delivered in combination with either CHOP (cyclophosphamide, doxorubicin, vincristine and prednisone; 33.1% of patients), CVP (cyclophosphamide, vincristine, prednisone; 9.8%) or bendamustine alone (B; 57.1%) as the chemotherapy backbone. The choice of regimen was at the discretion of the treating center.
A total of 1,202 patients with follicular lymphoma were enrolled and randomized to treatment and were included in an intention-to-treat analysis.
The treatment arms were well balanced with regard to distribution of patients characteristics, with approximately 21% in each arm having Follicular Lymphoma International Prognostic Index low-risk disease; 37% having intermediate-risk disease; and 34% having high-risk disease.
Roughly half of patients in each arm had bone marrow involvement, and two-thirds had extranodal involvement.
Obinutuzumab was dosed 1,000 mg IV on days 1, 8, and 15 of cycle one, and either on day 1 of cycles two through eight every 3 weeks, or every 4 weeks during cycles two through six.
Overall response rates at the end of induction were 86.9% with rituximab and 88.5% with obinutuzumab, with complete responses of 23.8% and 19.5%, respectively.
As noted before, investigator-assessed PFS favored obinutuzumab, as did PFS assessed by independent reviewer, at 81.9% vs. 77.9% for rituximab (HR, 0.71; P = .0138).
The newer antibody also had a slight edge in time to new treatment, with 87.1% of patients on obinutuzumab not starting on new therapy, compared with 81.2% of patients on rituximab.
More bendamustine deaths
Nearly all patients in each arm had an adverse event, with grade 3 or greater events occurring in 74.6% of patients on obinutuzumab vs. 67.8% on rituximab. Rates of neutropenia, leukopenia, febrile neutropenia, infusion reactions, and thrombocytopenia were all slightly higher with obinutuzumab. Grade 3 or greater infections occurred in 20% with obinutuzumab, compared with 15.6% with rituximab.
“What we did note, however, was a high level of mortality in patients receiving either obinutuzumab-based therapy or rituximab-based therapy, which were no different between the two arms and were somewhat higher than one might expect from patients receiving induction treatment in follicular lymphoma. Hence, we did a more detailed analysis of safety by treatment regimen,” Dr. Marcus said.
There were more deaths among patients treated with bendamustine (5.6% for patients in the B-obinutuzumab cohort, and 4.4% of patients in the B-rituximab cohort) vs. 1.6% and 2.0%, respectively, for patients on CHOP, and 1.6 and 1.8% for patients on CVP.
Dose effect?
John P. Leonard, MD, from Cornell University, New York , who introduced Dr. Marcus, commented that PFS may not be the ideal endpoint for patients with follicular lymphoma.
Dr. John P. Leonard
He pointed out that in trials comparing rituximab with obinutuzumab for other diseases, results have been mixed, with obinutuzumab showing superiority in chronic lymphocytic leukemia, but in data presented elsewhere at ASH 2016, obinutuzumab was not superior to rituximab for treatment of diffuse large B-cell lymphoma.
“One question is whether obinutuzumab, which is generally administered at a higher mg dose to patients, is in fact a better antibody or if it is in fact a dose effect,” he said.
In response to a similar question following his presentation, Dr. Marcus replied that, despite sharing a target, the two antibodies are different, with different mechanisms of action. He also noted that there is no evidence to suggest that rituximab potency would be greater in follicular lymphoma if it were given at higher doses.
The GALLIUM trial is sponsored by Hoffmann-La Roche, Dr, Marcus disclosed consulting with and receiving honoraria from the company, and relationships with other companies.