Primary pulmonary extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue type: a case report and literature review.

Primary pulmonary mucosa-associated lymphoid tissue (MALT)-derived lymphoma is a low-grade B-cell non-Hodgkin's lymphoma. It is rare with unclear clinical and imaging findings, requiring biopsy or surgery for diagnosis. Here, we provide a new case to learn the symptoms, diagnosis and treatment of primary pulmonary MALT lymphoma. The patient was a 51-year-old male. During the annual physical examination in 2019, a shadow in the lower lobe of the right lung was accidentally found in his chest computed tomography image. In 2020, the size and density of the shadows increased, which was suspected to be lung adenocarcinoma. The patient underwent video-assisted thoracoscopic surgery and segmental resection. Pathological examination showed residual germinal centers around the tumor cells, and many inflammatory cells had diffusely infiltrated, mainly monocyte-like B cells. Immunohistochemical analysis showed that CD3, CD20, Bcl-2, CD43, CK-pan and CD23 were positive, while BCL-6, CD5, CD10, c-myc and cyclin D1 were negative. The patient was diagnosed with MALT extranodal marginal zone B-cell lymphoma. The patient did not receive chemotherapy or radiotherapy after the operation but was still under close observation. Primary pulmonary MALT develops slowly and tends to be inert and spontaneous. Due to the lack of specific clinical symptoms and imaging findings, it can easily be misdiagnosed as tuberculosis, lung cancer, or infection. Thoracoscopic resection may be a good choice for the diagnosis and treatment.