Mosunetuzumab Successfully Treated Rituximab‐Refractory Lymphoma‐Associated Protein‐Losing Enteropathy With Concomitant Immune Thrombocytopenia in Follicular Lymphoma: A Case Report

Protein‐losing enteropathy (PLE) is a rare but potentially severe complication of malignant lymphoma characterized by excessive gastrointestinal loss of plasma proteins, leading to hypoalbuminemia, edema, and serous effusions. We report a case of follicular lymphoma complicated by severe PLE and concomitant immune thrombocytopenia (ITP) without gastrointestinal involvement. A 51‐year‐old man presented with progressive hypoalbuminemia, refractory ascites, thrombocytopenia, and systemic lymphadenopathy. Initial treatment with rituximab monotherapy was selected due to low tumor burden and ITP, followed by rituximab plus lenalidomide (R2), but both resulted in only transient responses. ^99m Tc‐labeled human serum albumin scintigraphy confirmed the diagnosis of PLE. Mosunetuzumab was initiated as third‐line therapy. Serum albumin levels increased from 0.7 g/dL to approximately 2.0 g/dL, accompanied by marked improvement in ascites and edema. Platelet counts, which had initially been reduced to approximately 30,000/µL, normalized after rituximab and further increased to 300,000–500,000/µL following mosunetuzumab. Complete remission was achieved and has been maintained for over four months at the time of writing. This case suggests that mosunetuzumab may effectively control both lymphoma‐associated PLE and immune‐mediated cytopenia through deeper and more sustained B‐cell depletion.

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