Isatuximab, bortezomib, lenalidomide, and limited dexamethasone in patients with transplant-ineligible multiple myeloma (REST): a multicentre, single-arm, phase 2 trial.

Background: Adding anti-CD38 monoclonal antibodies to standard therapies can improve outcomes in patients with multiple myeloma. Long-term treatment with corticosteroids increases the risk of infection. We aimed to evaluate the safety and activity of isatuximab, weekly bortezomib, lenalidomide, and limited dexamethasone in patients with newly diagnosed multiple myeloma ineligible for autologous haematopoietic stem-cell transplantation (HSCT).

Methods: REST is an academic, multicentre, single-arm, phase 2 trial of adults with newly diagnosed multiple myeloma and measurable disease as defined by International Myeloma Working Group criteria, ineligible for high-dose melphalan and autologous HSCT, Eastern Cooperative Oncology Group performance status of 0-3 (with 3 only allowed if related to myeloma). In 28-day cycles, patients received isatuximab (10 mg/kg intravenously on days 1, 8, 15, and 22 of cycle 1, and days 1 and 15 of cycles 2-18), bortezomib (1·3 mg/m subcutaneously on days 1, 8, and 15 of cycles 1-8), and lenalidomide (25 mg orally on days 1-21, until progressive disease). Dexamethasone was given 20 mg orally on days 1, 8, 15 and 22, limited to the two first cycles only. The primary endpoint was measurable residual disease (MRD)-negative complete response, assessed by next-generation flow cytometry (sensitivity 1·0 × 10), during or after 18 cycles of study treatment. MRD was tested in all patients who had at least complete response before cycle 19 and in all patients who had at least very good partial response at cycle 19. All patients enrolled initiated treatment and were included in the analyses. This trial is registered with ClinicalTrials.gov (NCT04939844); the primary endpoint is reported in this Article, and follow-up is ongoing.

Findings: Between June 30, 2021 and Jan 19, 2023, we assessed for eligibility and recruited 51 patients (27 [53%] females and 24 [47%] males), with a median age of 77 years (IQR 73·5-80). 39 participants completed 18 cycles of treatment on protocol, of whom two had discontinued treatment but not protocol. At a median follow-up of 27·0 months (IQR 23·0-33·7), MRD-negative complete response was observed in 19 (37% [95% CI 25·3-51·0]) patients, with a median treatment duration of 22 months (IQR 15·2-28·8; range 1·4-35·1). Disease progression or death had occurred in 18 (35%) of 51 patients, and eight (16%) patients had died. During the first 18 cycles of study treatment, the most common adverse events of grade 3 or 4 were neutropenia (28 [55%] patients), infections (21 [41%] patients), and thrombocytopenia (11 [22%] patients). 48 serious adverse events of grade 3 or higher were reported in 27 (53%) patients. A total of 14 (27%) patients discontinued treatment before cycle 19, most commonly because of progressive disease (eight [16%]) and adverse events (four [8%]). Two deaths (one due to pneumonia and one due to sepsis) were assessed as possibly related to study treatment.

Interpretation: Isatuximab, weekly bortezomib, and lenalidomide with limited dexamethasone was active and safe as initial therapy for older patients with multiple myeloma ineligible for autologous HSCT. A modified quadruplet regimen in which dexamethasone is omitted after two cycles can be used in this patient population.

Funding: Sanofi.