LUGANO, SWITZERLAND – The chemotherapy-free combination of ibrutinib (Imbruvica) and rituximab is highly effective as frontline therapy for older, transplant-ineligible patients with nonblastoid mantle cell lymphoma, according to investigators.
In aof patients with a median age of 71 years, 38 of 41 patients (93%) had an objective response, and the regimen was both safe and easy to administer, reported Preetesh Jain, MD, PhD, of the University of Texas MD Anderson Cancer Center in Houston.
“The adverse event profile was generally favorable, with specific monitoring recommended for patients with cardiovascular comorbidities and a history of atrial fibrillation,” he said at the International Conference on Malignant Lymphoma.
The investigators enrolled 48 patients aged 65 years and older with previously untreated mantle cell lymphoma (MCL), of whom 41 were evaluable for the primary endpoints of overall response rate (ORR) and safety. The patients had good performance status and normal organ function, with the largest tumor size less than 10 cm. Patients with atrial fibrillation could participate, if the fibrillation was controlled. Patients with Ki-67 protein levels of 50% or greater and blastoid/pleomorphic histology were excluded.
Patients were treated with ibrutinib 560 mg orally daily for each 28-day cycle, with therapy continued until disease progression, or until therapy was stopped for any other reason. Patients also received intravenous rituximab 375 mg/m2 on days 1, 8, 15 and 22, plus or minus one day for cycle 1, on day 1 of cycles 3-8, and on day 1 of every other cycle for up to 2 years.
Of the 41 patients evaluable for response, 26 (64%) had a complete response (CR) and 12 (29%) had a partial response. Three additional patients had stable disease, for an objective response rate of 93%.
Of 34 patients with PET scans, all had negative scans. Of 37 patients evaluable for minimal residual disease (MRD) by flow cytometry, 21 (58%) were MRD negative.
Patients with low or intermediate Mantle Cell Lymphoma International Prognostic Index (MIPI) scores had a higher ORR (100% vs. 89% for patients with high MIPI scores), and patients with low Ki-67 levels had a higher response rate than that of patients with KI-67 of 30% or greater (80% vs. 87%).
Neither median 3-year progression-free survival nor median 3-year overall survival have been reached, with respective 3-year rates of 87% and 95%.
Four patients experienced disease progression at 4, 10, 13 and 33 months of treatment. Three of these patients had disease that had transformed to blastoid/pleomorphic variant, two had Ki-67 of 30% or greater, one had mutations in TP53, and one had FAT1 and SF3B1 mutations.
Two patients died after ibrutinib therapy, one who had discontinued therapy because of bleeding, and the other who died on treatment at 13 months from transformed disease. Both of these patients had high Ki-67 levels.
Grade 3 or 4 hematological adverse events were neutropenia in four patients, and thrombocytopenia in two patients. There were no cases of grade 3 or 4 anemia.
Grade 3 or 4 nonhematological adverse events were fatigue, myalgia, and atrial fibrillation in seven patients each, diarrhea in six patients, and petechiae/bleeding in three patients.
Patients will continue to be followed for late adverse events, secondary cancers, and relapses, and further studies on clonal evolution, mutation profiling, and MRD are ongoing and will be reported at a later date, Dr. Jain said.
The National Cancer Institute supported the study. Dr. Jain reported having no financial disclosures.
SOURCE: Jain P et al. 15-ICML. Abstract 011.