Ibrutinib in Combination With Rituximab for Indolent Clinical Forms of Mantle Cell Lymphoma (IMCL-2015): A Multicenter, Open-Label, Single-Arm, Phase II Trial

[Puropose]: The need for an individualized management of indolent clinical forms in mantle cell lymphoma (MCL) is increasingly recognized. We hypothesized that a tailored treatment with ibrutinib in combination with rituximab (IR) could obtain significant responses in these patients.
[Methods]: This is a multicenter single-arm, open-label, phase II study with a two-stage design conducted in 12 Spanish GELTAMO sites (ClinicalTrials.gov identifier: NCT02682641). Previously untreated MCL patients with indolent clinical forms defined by the following criteria were eligible: no disease-related symptoms, nonblastoid variants, Ki-67 < 30%, and largest tumor diameter ≤ 3 cm. Both leukemic non-nodal and nodal subtypes were recruited. Patients received ibrutinib 560 mg once daily and a total of eight doses of rituximab 375 mg/m2. Ibrutinib could be discontinued after 2 years in the case of sustained undetectable minimal residual disease (MRD). The primary end point was the complete response (CR) rate achieved after 12 cycles according to Lugano criteria.
[Results]: Fifty patients with MCL (male 66%; median age 65 years) were enrolled. After 12 cycles of treatment, 42 (84%; 95% CI, 74 to 94) patients had an overall response, including 40 (80%; 95% CI, 69 to 91) with CR. Moreover, undetectable MRD in peripheral blood was achieved in 87% (95% CI, 77 to 97) of cases. At 2 years, 24 of 35 evaluable patients (69%) could discontinue ibrutinib because of undetectable MRD. Four patients had disease progression; three were non-nodal MCL and carried high genomic complexity and TP53 mutations at enrollment. No unexpected toxicity was seen except one patient with severe aplastic anemia.
[Conclusion]: Frontline IR combination achieves a high rate of CRs and undetectable MRD in indolent clinical forms of MCL. Discontinuation seems appropriate in cases with undetectable MRD, except for TP53-mutated cases.
The authors would like to thank the patients and their families, and study investigators and coordinators—among them, Carlos Grande, Lucia Palacios, and Silvia Ru´ız—for their contribution to the study. Partial support of biological and MRD studies was obtained from grants Instituto de Salud Carlos III (ISCIII) PI19/00887 (to A.L.-G. and E.G.) and PI17/ 01061 (to S.B.), Fundacio La Marat ´ o de TV3 grant 201904-30 (to S.B.), ´ Ministerio de Ciencia e Innovacion (MCI) RTI2018-094274-B-I00 (to ´E.C.), National Institutes of Health (NIH) 1P01CA229100 (to E.C.) and FEDER: European Regional Development Fund “Una manera de hacer Europa” (to E.C. and S.B.). A personal grant FEHH-Janssen 2021 to Alejandro Medina-Herrera from Fundacion Española de Hematología y Hemoterapia is acknowledged. E.C. is an ICREA Academia Researcher