Extranodal lymphoma of low grade malignancy-including lymphoma of mucosa-associated lymphoid tissue(MALT).

Abstract

Malignant lymphoma (ML) of low grade malignancy includes small lymphocytic lymphoma and follicular lymphoma other than large cell type. Recent study revealed intermediate lymphocytic lymphoma (ILL) and monocytoid B-cell lymphoma (MBCL) to be new types of ML of low grade malignancy. These two types of ML are fundamental elements of ML developing in so-called mucosa associated lymphoid tissue (MALT). In this report, results of our study on ILL and MBCL of extranodal organs were described.ILL is composed of small lymphoid cells with morphologic features between those of well-differentiated lymphocytic lymphoma and poorly differentiated lymphocytic lymphoma of follicular center cell origin. The frequency of ILL in nodal and extranodal non-Hodgkin's lymphoma was almost same. The frequency was high in salivary gland and thyroid lymphoma. Histologic features of chronic lymphocytic thyroiditis (CLTH) are constantly observed in cases with thyroid lymphoma. Histologic findings suggestive of Sjogren's syndrome such as formation of lymphoid follicles and myoepithelial islands were observed in one third of cases with salivary lymphoma. These findings suggested that autoimmune diseases such as CLTH and Sjogren's syndrome played an important role in the etiology of thyroid and salivary lymphoma.MBCL shows the proliferation of the atypical lymphoid cells with abundant and pale cytoplasm and reniform nucleus. The high incidence of Sjogren's syndrome in cases with MBCL was evident suggesting the etiologic role of Sjogern's syndrome for development of MBCL. Six cases of MBCL developing in extranodal sites such as thyroid, stomach, and rectum were described below. Two of three patients with thyroid lymphoma presented with positive serum antithyroid antibodies, and one had CLTH. In all three patients with gastric or rectal lymphoma, reactive lymphoid hyperplasia was present near the tumors. These findings suggested the important role of long-standing inflammation for development of MBCL as well as ILL.