Patterns of presentation, treatment, and survival in primary mediastinal B cell lymphoma: A colombian retrospective cohort

Abstract Introduction: Primary mediastinal B-cell lymphoma (PMBCL) is a rare and aggressive subtype of diffuse large B-cell lymphoma (DLBCL), accounting for 5-10% of all cases, with unique clinical and molecular characteristics that lead to significant therapeutic controversies (Renaud et al., 2025). Due to its rarity, there is scarce evidence regarding this disease, particularly in resource-limited settings such as Colombia. The current study aims to characterize disease features, treatment access, and survival in primary mediastinal lymphoma in Bogotá, Colombia. Methods: We conducted a retrospective, observational study at Fundación Santa Fe de Bogotá (Bogotá, Colombia), including patients with PMBCL diagnosed between 2005 and 2025. Clinical and treatment-related data were extracted from electronic medical records, including baseline characteristics, clinical and molecular presentation, treatment patterns and survival outcomes. Descriptive statistics were used to summarize patient characteristics. The primary outcome was 5-year overall survival (OS), which was analyzed using Kaplan–Meier estimates, and associations between biomarker-defined subgroups and OS were evaluated using Cox proportional hazards regression. Comparisons were made with real-world series. Results: A total of 19 patients were included. The average age was 61 (SD 11.8) years and 57,9% (n = 11) were male. Early-stage disease was common (36.8%, n =, stage 2), and the average IPI classification was 1.22 (SD 1.2) with a median Ki-67 value of 42% (IQR: 70-41). 25% (n = 4) presented with pleural effusion, 12.5% had superior vena cava syndrome (n=2) and 6.25% had pericardial effusion (n=1).At the time of diagnosis, 66.6% had extranodal involvement, Ki-67% was 42 (56.7-30) and (35%, n=5) had LDH above the upper limit of normal. Molecular features varied considerably along the cohort; CD20 expression was detected in 29.4% (n = 5), CD10 in 17.6% (n=3), CD30 in 11.7% (n = 2). None of the patients in this cohort had access to NGS. R-CHOP protocol was the most common induction regimen (58.8%, n =10) followed by ABVD (23.5%, n=4), Bortezomib combined with Rituximab-Mitoxantrone (11.7%, n=2) and ICE (5,8%, n=1). 10 patients had complete remission during their first line (58.8%) and 5 had a partial response (29.4%). In second and third-line settings both complete remission and partial response was registered at 33.3%. For upfront treatment 21,1% (n=4) received consolidation radiotherapy, (11.7%,n=2) were consolidated with autologous stem cell transplant (ASCT), and (23.5%, n=4) received radiotherapy alone. At a median follow-up of 5.17 years (range 0.33 - 17.33), the estimated one year overall survival was 89.2 % (95 % CI 63.1–97.2), and three and five year overall survival remained stable at 89.2 % (95 % CI 63.1–97.2). After 10 years, overall survival declined to 70.2 % (95 % CI 36.6–88.3). Compared with emerging evidence, our cohort demonstrated comparable early outcomes but a more pronounced decline at extended follow-up (Guven et al., 2021; Savage, 2022; Zinzani et al., 2019). Likewise, there was a significant lack of access to Nivolumab and Brentuximab Vedotin, which has shown promising early efficacy in patients with R/R PMBCL as has been described in large clinical trials such as CheckMate 436 (Zinzani et al., 2019). Conclusions: This small single center retrospective cohort study is one of the first to be conducted regarding PMBL in Latin America and to our knowledge first conducted in Colombia. Our findings regarding survival suggest efficient disease control, however with a high risk for late relapse beyond five years. In that sense, larger local real world studies are needed and it is crucial to emphasize on diagnosis and treatment strategies used in this region in order to optimize clinical outcomes in resource limited settings.