Pembrolizumab as an Unconventional First-line Salvage Therapy in Primary Mediastinal Large B-cell Lymphoma: A Case Report

Abstract Primary mediastinal large B-cell lymphoma (PMBCL) is a rare and aggressive subtype of non-Hodgkin lymphoma with unique clinical and molecular characteristics. We report the case of a young woman diagnosed with PMBCL who presented with a bulky mediastinal mass and responded favorably to pembrolizumab monotherapy after initial R-CEOP treatment was discontinued due to adverse effects. Over 24 months of follow-up, pembrolizumab monotherapy, later combined with rituximab, achieved a complete response and gradual clinical improvement. Despite experiencing severe complications throughout the clinical course, the patient demonstrated an excellent therapeutic response to immune checkpoint inhibitor monotherapy, underscoring the potential clinical value of this treatment approach.