Monocytoid B-cell lymphoma. Clinicopathologic study of 21 cases of a unique type of low-grade lymphoma.

The morphologic and immunologic features of three cases of an unusual and distinct B-cell lymphoma were recently described and termed monocytoid B-cell lymphoma (MBCL) because of the striking resemblance of the neoplastic cells to reactive monocytoid B-lymphocytes. The morphologic spectrum and the clinical behavior of MBCL were investigated in a series of 21 patients. This study indicates that patients with MBCL usually present with lymphadenopathy and Stage I or II disease. MBCL also occurs at extranodal sites including the salivary gland. Because four of the patients with MBCL had Sjögren's syndrome with characteristic laboratory profiles, these results raise the possibility that there may be a relationship between MBCL and Sjögren's syndrome. Eight patients were male and 13 female (M:F = 1:1.6), and MBCL primarily involved the elderly (median age, 66 years). The most striking clinical findings were high percentages of complete remissions and long survival times indicating that MBCL is a low-grade lymphoma. Of 21 patients investigated, 18 were in complete remission at the time of completion of this study. Two patients died with the disease and one was lost to follow-up. Patients with localized MBCL may have a better survival rate than those with generalized disease. Like other low-grade lymphomas, MBCL can progress to a higher grade lymphoma of large cell type. Unlike other low-grade lymphomas, in MBCL splenomegaly, bone marrow involvement, and leukemic conversion are uncommon.