Treatment was stopped in the single-arm phase 2 trial when patients reached undetectable MRD, a novel use of MRD to guide treatment duration. At a median of 16 months after discontinuation, MRD remained undetectable in 31 of 33 patients (94%).
The team also found that a reduction to 1/400 of baseline MRD (delta-MRD400) by day 1 of cycle five predicted undetectable bone marrow MRD within eight treatment cycles.
delta-MRD400 is “a potential biomarker” to identify patients who’ll do well with a shorter treatment and flag others who require longer courses of therapy, said investigators led by Jacob Soumerai, MD, a hematologist/oncologist at Massachusetts General Hospital, Boston.
Overall, the results “are highly encouraging,” they said, with efficacy and safety comparing favorably to trials that added other BTK inhibitors – namely ibrutinib and acalabrutinib – to the standard obinutuzumab/venetoclax backbone, with a shorter treatment duration.
They said the novel triplet warrants further study in the first line and noted that they also “plan to prospectively validate early-MRD-response kinetics as a biomarker to guide treatment duration.” The study was published recently in The Lancet Haematology.
Two editorialists – Davide Rossi, MD, PhD, and Joyce Marques De Almeida, both of the of the Oncology Institute of Southern Switzerland, Bellinzona – were encouraged by the findings and wanted future research to assess how well MRD-guided treatment duration works in patients with tumor protein p53-disrupted disease, who “benefit less from time-limited therapies” then patients with wild-type TP53; the trial was too small to address the issue.
There was a two-cycle lead-in with zanubrutinib and obinutuzumab then venetoclax ramp-up starting at cycle 3, with each cycle running 28 days.
Zanubrutinib is approved in the U.S. for mantle cell lymphoma, Waldenström’s macroglobulinemia, and marginal zone lymphoma.
In a previous phase 2 trial of ibrutinib add-on to venetoclax-obinutuzumab for 14 cycles followed by ibrutinib monotherapy, the rate of undetectable MRD in both peripheral blood and bone marrow was 67%. The rate of bone marrow undetectable MRD was 77% in another phase 2 trial of acalabrutinib, venetoclax, and obinutuzumab for at least 15 cycles.
Dr. Soumerai and his team cautioned, however, that “comparisons across trials are fraught with selection bias resulting in differences in treated patient populations, and randomized data are needed to establish the optimal BTK inhibitor to combine with venetoclax with or without obinutuzumab, and to establish whether” the zanubrutinib triplet “improves progression-free survival and overall survival compared with current standard first-line therapy.”
There was grade 3 or worse neutropenia in 18% of subjects (7/39), one episode of febrile neutropenia (3%), lung infections in three patients (8%) patients, and five cases of hypertension (13%).
The editorialists characterized the numbers as low and the regimen as well tolerated. Past studies of ibrutinib, a first generation BTK, with venetoclax and obinutuzumab have pegged grade 3 or worse neutropenia at 56% and the hypertension incidence at 48%.
Granulocyte colony-stimulating factor administration “could partially account for the low incidence of severe neutropenia” in the trial, the investigators said.
The study was funded by zanubrutinib marketer Beigene as well as Genentech, the National Cancer Institute, and others. Many of the authors had industry ties, including Dr. Soumerai who reported being a consultant and researcher for Beigene and other companies. Dr. Rossi reported honoraria and research grants from AbbVie, AstraZeneca, and Janssen.