Clinicopathological Features of Primary Mediastinal Large B-cell Lymphoma: A 5-Year Retrospective Study

Objective: To describe the clinicopathological features and treatment outcomes of primary mediastinal large B-cell lymphoma (PMBCL) at Siriraj Hospital, Thailand. Materials and Methods: This retrospective study included all patients diagnosed with PMBCL during 2020-2024. Clinical, pathological, treatment, and survival data were retrieved from medical records and pathology reports. Overall survival (OS) and progression-free survival (PFS) were estimated using the Kaplan-Meier method. Results: PMBCL accounted for 37 of 74 mediastinal lymphoma cases (50%). Median age was 29 years (IQR: 22-32), with female predominance (62.2%). Presentations included cough (79.4%), dyspnea (74.3%), and SVC syndrome (51.4%). Pleural or pericardial effusion was found in 75.0%. Bulky disease (>10 cm) and elevated LDH were 75.7% and 91.4%, respectively. Histologically, sclerotic pattern and HRS-like cells were observed in 41.7% and 31.4%, respectively. All cases were CD20-positive; CD23 and CD30 were expressed in 65.5% and 80.6%, respectively. A non-GCB phenotype was identified in 64.5% by the Hans algorithm. DA-EPOCH-R was the most common first-line regimen (63.9%). At a median follow-up of 25 months, the 24-month OS and PFS rates were 80.1% and 66.8%, respectively. Conclusion: This study provides the first characterization of PMBCL in a Thai cohort, showing frequent SVC syndrome and pleural or pericardial effusion at diagnosis. Given the overlapping features and complexity of differential diagnosis, comprehensive immunohistochemical workup was essential for accuracy. DA-EPOCH-R was the dominant first-line therapy, with 2-year outcomes comparable to the rituximab era. Prompt recognition, diagnostic expertise, and multidisciplinary management are critical for optimizing PMBCL outcomes.