Syndrome of Inappropriate Antidiuretic Hormone Secretion in a Patient with Mucosa-associated Lymphoid Tissue Lymphoma

: Syndrome of inappropriate antidiuretic hormone secretion (SIADH) may develop in association with several malignancies. However, as an immunohistochemical analysis is not performed in the majority cases, its true cause is often uncertain. We herein report a case of SIADH following chemotherapy due to tumor-derived ADH production in a patient with mucosa-associated lymphoid tissue (MALT) lymphoma. A retrospective immunohistochemical analysis demonstrated ADH expression by lymphoma cells. These findings highlight the importance of using an immunohistochemical analysis to determine ADH production by tumor cells in patients with SIADH. Such analyses play an important role in elucidating the pathogenesis of SIADH and determining the most appropriate treatment.