Extranodal Marginal Zone Lymphoma of Mucosa Associated Lymphoid Tissue (MALT LYMPHOMA) With Extensive Plasma Cell Differentiation and Localized Amyloid Deposition.

Abstract

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT) lymphoma is a mature and clinically indolent B cell lymphoma composed of heterogeneous cell population. Plasma cell differentiation is commonly seen in MALT lymphomas. However, plasmacytic differentiation along with localized amyloid deposition in the lungs is an extremely rare. We encountered a unique case of Extranodal MALT lymphoma with extensive plasmacytic differentiation and amyloid deposition. A 78-year-old female with past history of Gastric MALT lymphoma, status post chemotherapy presented in outpatient clinic. PET scan revealed an incidental 9 mm nodule in left lung, and subsequently underwent biopsy. Histology showed sheets of heterogeneous neoplastic cells including small lymphocytes, monocytoid cells, and abundant number of plasma cells (Fig A) in the background of hyalinization (Fig B). Immunohistochemical (IHC) reveals lymphoma cells are positive for CD20 (Fig C) and CD43, and plasma cells showed lambda restriction (Fig D). Furthermore, Congo Red stain of eosinophilic background showed positive birefringence upon polarization, consistent with Amyloid. Great caution is required in differentiating these cases from lymphoplasmacytic lymphoma as the histologic and IHC features can significantly overlap, and studies have also suggested that plasmacytic differentiation in these cases represent precursor neoplasm of plasma cells. Amyloid depositions in MALT lymphomas are rare and organ confined but can lead to local complications and cause considerable morbidity. Therefore, it is necessary to be aware of the association between MALT lymphoma with extensive plasma cell differentiation and amyloid deposition, as close clinical follow up is recommended.