Adding ibrutinib to chemotherapy did not improve outcomes for children and young adults with relapsed or refractory mature B-cell non-Hodgkin lymphoma (B-NHL), an interim analysis of the SPARKLE trial showed.
Among 51 patients aged 1-30 years with mature B-NHL that had been diagnosed before age 18, there was no significant difference in the primary endpoint of event-free survival (EFS) between patients assigned on a 2:1 basis to receive either ibrutinib (Imbruvica) plus one of two chemotherapy regimens or to chemotherapy alone. In fact, EFS was shorter among patients assigned to ibrutinib, although a larger proportion of these patients had previously received rituximab, a known factor for poor prognosis, reported Amos Burke, MD, from Cambridge (England) University.
The trial was stopped for futility in May 2020, after a median follow-up of 17.97 months.
“Further studies are required to determine the optimal therapy for patients with relapsed, mature B-NHL, especially those who have received prior rituximab,” he said in an audio walk-through of a scientific poster presented during the annual meeting of the American Society of Pediatric Hematology/Oncology.
“This is a very challenging patient population because they historically have had a very poor survival rate,” commented Paul J. Galardy, MD, a pediatric hematologist/oncologist at the Mayo Clinic in Rochester, Minn., who was not involved in the study.
“The field has struggled to improve outcomes for these patients in part because there are relatively few patients per year with relapsed refractory mature B-cell lymphoma due to the very effective nature of the up-front therapy. This makes new clinical trials difficult to perform,” he said.
Poor prognosis
Ibrutinib, an inhibitor of Bruton tyrosine kinase, is approved in the United States for treatment of marginal zone lymphoma, mantle cell lymphoma, and chronic lymphocytic leukemia/small lymphocytic lymphoma, as well as other indications, all in adults only. It has also been shown to have activity against B-NHL in preclinical and early human trials, Dr. Burke said.
Given the poor prognosis of children and young adults with relapsed/refractory mature B-NHL – a 2-year overall survival (OS) of 30% or less with chemoimmunotherapy – the investigators tested whether adding ibrutinib to the standard of care could improve outcomes.
They enrolled patients with relapsed/refractory B-NHL in first relapse or primarily refractory to conventional therapy, with measurable disease (greater than 1 cm) by CT, bone marrow involvement, or cerebrospinal fluid with blasts. The patients were required to have Karnofsky-Lansky performance scores of 50 or greater.
The histologies included Burkitt lymphoma, diffuse large B-cell lymphoma (DLBCL), Burkitt-like lymphoma, Burkitt leukemia, primary mediastinal B-cell lymphoma, and other unspecified types.
Dr. Burke reported results on 48 patients included in the May 2020 analysis, plus 3 additional patients who were enrolled between the data cutoff for the first analysis and the meeting of the independent data monitoring committee where the decision was made to stop the trial.
A total of 35 patients were randomized to receive ibrutinib with either the RICE (rituximab plus ifosfamide, carboplatin, and etoposide) or RVICI (rituximab plus vincristine, ifosfamide, carboplatin, idarubicin, and dexamethasone) regimen. All of these patients received treatment on study.
Of the 18 patients randomized to receive either RICE or RVICI alone, 1 did not receive any cycles of chemoimmunotherapy.
At the data cutoff for the updated analysis in November 2020, 14 patients assigned to ibrutinib and 4 assigned to chemoimmunotherapy alone remained on study; no patients in either arm were still receiving therapy.
A total of 17 patients assigned to the combination arm died and 4 withdrew consent. In the chemoimmunotherapy-alone arm, 10 died and 2 withdrew consent.
In both arms, patients were treated until either completing three cycles of therapy, start of conditioning treatment prior to stem cell transplantation, disease progression, or unacceptable toxicity.
In the ibrutinib arm, the median EFS was 5.36 months, compared with 6.97 months with chemoimmunotherapy alone, translating into a hazard ratio for EFS with ibrutinib of 1.078 (nonsignificant).
The respective median overall survival was 13.44 versus 11.07 months,
Subgroup analysis showed that EFS and OS did not differ significantly by age, histology, background regimen, or central nervous system or bone marrow involvement.
Overall response rates were 68.6% in the ibrutinib arm, and 81.3% in the chemoimmunotherapy arm. The respective complete response rates were 8.6% and 18.8%, and partial response rates were 60% and 62.5%.
The overall treatment-emergent adverse event (TEAE) profile was similar between the treatment arms, although six patients in the ibrutinib arm versus one in the chemoimmunotherapy arm experienced a major hemorrhage. One patients in the ibrutinib arm died from pulmonary hemorrhage.
Dr. Burke noted that, although the numbers were small, the failure to see a difference in efficacy between study arms may have been caused in part by a greater number of patients assigned to ibrutinib who had received prior treatment with rituximab (85.7% vs. 56.3%).