Uncovering the Epidemiology, Therapy Patterns and Outcomes of MALT Lymphoma in Latin America: A Multinational Retrospective Cohort Study

Introduction Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT) is characterized by slow progression and generally good prognosis. This type of non-Hodgkin lymphoma is often linked to chronic inflammatory conditions such as infections (e.g. H pylori in gastric MALT) or autoimmune disorders like Sjögren's syndrome. The prevalence and risk factors associated with MALT lymphoma can vary significantly across different regions of the world. In developing countries, including those in Latin America (LATAM), the epidemiology and treatment patterns for MALT lymphoma have been less studied. To address these gaps, we conducted a retrospective study across LATAM, focusing on the clinical features, treatment modalities, and survival outcomes of MALT lymphoma. Methods We conducted a retrospective cohort study of patients (pts) aged ≥18 years with newly diagnosed MALT lymphoma between 2001-2023 across 12 LATAM countries. Patient data were manually extracted from medical records on a standardized form. Primary endpoint was overall survival (OS) defined as time from diagnosis to death from any cause, while secondary endpoint was progression-free survival (PFS) defined as time from diagnosis to relapse, disease progression or death from any cause. Kaplan-Meier and Log-rank tests were used to estimate and compare survival probabilities. Results We enrolled 308 pts. The median age at diagnosis was 62 years (54% >60 years; range 23-93), with a slight female predominance (59%). Non-gastric MALT was the most common clinical presentation (n=191, 62%) with ocular adnexa (34%) being the most common extranodal site. Of the 117 (38%) gastric MALTs, 66% (n=79) were associated to H pylori infection. Overall, localized disease (stages I-II) was the most frequent presentation at diagnosis (n=226, 76%). Advanced stage was common in pts >60 years (66% vs 34% in ≤60 years, p=0.022). Watch and wait was offered to 12 (4%) pts. Single-agent rituximab was commonly used in localized stage (33% vs 12%, p<0.01) whereas immunochemotherapy was primarily used in advanced stage (49% vs 31%, p<0.01). R-CHOP was the most common immunochemotherapy regimen used (n=53, 28%). First-line radiotherapy (RT) alone was offered to only 63 (21%) pts with localized disease, while combined modality (i.e. systemic therapy plus RT) was administered to 17 (6%) pts with advanced (n=3) or localized disease (n=14). The median RT dose was 24 Gy (4-40). All H pylori-associated MALT received antibiotics, whereas only 6 (n=6/106, 5%) ocular adnexa MALTs received empiric antibiotic therapy (only 1 case was positive for Chlamydia psittaci). Response to therapy was available in 23 pts, the overall response rate to any approach was 95% (complete response, CR 78%) and 100% (CR 80%) for localized and advanced stage, respectively. Higher CRs were observed in gastric (86%) than non-gastric MALT (67%). With a median follow-up of 50.1 months (37-55), the median OS and PFS in all pts were not reached. The 4-year OS and PFS rates were 91% and 76%, respectively. Worse OS (86% vs 94%, p=0.042) and PFS (63% vs 85%, p<0.001) were observed in pts with gastric than non-gastric MALT, respectively. Worse OS (78% vs 95%, p<0.001) and PFS (59 vs 81%, p=0.001) were also observed in pts with advanced than localized stage disease, respectively. None first-line approach conferred OS or PFS advantage. Conclusion In this large cohort of MALT lymphoma pts from LATAM, our findings reveal a distinct distribution of MALT cases with a predominance of female pts and high incidence of non-gastric MALT, particularly ocular adnexa, suggesting unique environmental and possibly genetic factors influencing lymphoma risk in this region. Our study also highlights significant differences in treatment patterns. Rituximab monotherapy was commonly used for localized MALT, while immunochemotherapy, particularly R-CHOP, was prevalent in advanced stages. The limited use of RT in localized disease could reflect challenges in healthcare infrastructure. Worse outcomes were noted in pts with gastric MALT and those with advanced-stage disease, underscoring the need for tailored therapeutic strategies. Prospective evaluations are ongoing to better understand therapy patterns, access to novel treatments, and the etiological reasons behind the high incidence of non-gastric MALT in this cohort.