Background
Phase III, 3-arm RCT. 454 patients with untreated extranodal MALT lymphoma (gastric and non-gastric sites). Compared chlorambucil monotherapy, rituximab monotherapy, and the combination of rituximab + chlorambucil (R+Clb). IELSG-19 is the pivotal randomized trial establishing standard frontline therapy for MALT lymphoma.
Interventions and follow up
Arm A: Rituximab 375mg/m² IV weekly × 4, then at months 3, 5, 7, 9 (total 8 doses)
Arm B: Chlorambucil 6mg/m² PO daily × 42 days (6 weeks), repeated every 6 months × 4 cycles
Arm C: Rituximab 375mg/m² IV (same schedule as Arm A) + chlorambucil 6mg/m² PO (same schedule as Arm B)
Primary endpoint: Event-free survival
mFollow up: ~7.4 years
Arm B: Chlorambucil 6mg/m² PO daily × 42 days (6 weeks), repeated every 6 months × 4 cycles
Arm C: Rituximab 375mg/m² IV (same schedule as Arm A) + chlorambucil 6mg/m² PO (same schedule as Arm B)
Primary endpoint: Event-free survival
mFollow up: ~7.4 years
Results
5-year EFS: 68% (R+Clb) vs 51% (chlorambucil) vs 50% (rituximab), HR 0.54 (R+Clb vs Clb), P=.0009
5-year OS: ~90% across all 3 arms — no OS difference
ORR: 96.3% (R+Clb) vs 92.4% (Clb) vs 88.7% (R)
CR rate: 78.4% vs 65.5% vs 65.0%
5-year OS: ~90% across all 3 arms — no OS difference
ORR: 96.3% (R+Clb) vs 92.4% (Clb) vs 88.7% (R)
CR rate: 78.4% vs 65.5% vs 65.0%
Adverse events
Hematologic: Grade ≥3 neutropenia R+Clb 22.4%, chlorambucil 12.3%, rituximab 3.7%; grade ≥3 infections uncommon in all arms; no treatment-related deaths
Infusion: Rituximab-related infusion reactions 11.7% (R+Clb arm)
Infusion: Rituximab-related infusion reactions 11.7% (R+Clb arm)
Conclusions
Rituximab + chlorambucil significantly improved 5-year EFS versus either agent alone in extranodal MALT lymphoma, establishing the R+Clb combination as the standard frontline regimen for patients requiring systemic therapy. OS was identical across arms, reflecting the indolent nature of MALT lymphoma and effective salvage options.
Key Limitations
No OS benefit — EFS is a surrogate endpoint in an indolent disease. Many MALT lymphoma patients can be managed with local therapy (radiation, H. pylori eradication for gastric MALT) without systemic chemotherapy, limiting the population to whom these results apply. Chlorambucil is being replaced in clinical practice by bendamustine in many centers, though no direct randomized comparison exists. The long-term risk of secondary myeloid neoplasms with chlorambucil is not trivial in a disease with excellent OS.
Clinical Context
Rituximab + chlorambucil is an established frontline option for systemic therapy in MALT lymphoma. For gastric MALT: H. pylori eradication achieves CR in ~76% and is first-line for H. pylori-positive disease; the t(11;18) translocation predicts antibiotic resistance. Non-gastric MALT (ocular adnexal, salivary gland, lung) is often treated with radiotherapy if localized. BTK inhibitors (ibrutinib, zanubrutinib — MAGNOLIA) are now approved for R/R MZL including extranodal MALT.