Primary extranodal marginal zone B-cell lymphoma with AL amyloidosis in cerebral parenchyma in an immunocompetent patient

Herein reported is an extremely rare case of primary MALT lymphoma of cerebral parenchyma. A 79-year-old man presented with paresis. Imaging modalities identified a tumor measuring 3 cm in diameter in right cerebral parenchyma. An operation completely resected the tumor. Macroscopically, the tumor was well defined, but showed mild infiltrative features. Histologically, the tumor showed proliferation of small atypical lymphocytes separated by fibrous septae with AL amyloid depositions. No apparent plasma cell differentiation was seen. The tumor cells showed monotonous appearances with hyperchromatic nuclei but without nucleoli and nuclear indentations. Immunoblastic cells were scattered. Immunohistochemically, tumor cells were positive for vimentin, CD45, CD20, CD79α, bcl-2, CD3 (focal), CD45RO (focal), CD5 (focal), CD10, CD23, bcl-6, CD138, p53, and Ki-67 (labeling = 27%). The immunoblastic cells were positive for CD30. The lymphoid cells were negative for Epstein–Barr virus (EBV)-related molecules of EBV latent membrane protein-1 (LMP-1) and EBV early RNAs (EBER). They were also negative for cytokeratins AE 1/3 and CAM5.2, cyclin D1, CD34, GFAP, α-smooth muscle actin, and S100 protein. Because of the heterogeneity of tumor cells and positive AL amyloid deposition, the author diagnosed it as primary MALT lymphoma. The patient is now free from tumors. Differential diagnosis was discussed.