Is lymphoplasmacytic lymphoma/immunocytoma a distinct entity? A clinicopathologic study of 20 cases

Lymphoplasmacytic lymphoma/immunocytoma (LLI) was defined initially as a sm all B-cell lymphoma with plasmacytoid or plasmacytic features. Because othe r types of small B-cell lymphoma, particularly marginal zone B-cell lymphom a may exhibit plasmacytic differentiation, the revised European-American ly mphoma classification and World Health Organization has defined LLI more na rrowly to exclude other small B-cell lymphomas. The goal of this study was to reevaluate LLI as a clinicopathologic entity. Twenty cases were selected from 43 previously diagnosed as "small lymphocytic lymphoma, plasmacytoid" or "immunocytoma" from 1985 to 1998. Cases fulfilling the criteria for B-c ell small lymphocytic lymphoma, follicular lymphoma, marginal zone B-cell l ymphoma, or other types of B-cell lymphoma were excluded. The histopatholog y and immunoreactivity for CD20, CD79a, CD3, CD43, CD23, CD5, kappa, lambda , and immunoglobulins (Ig's) M, G, and A were reviewed, in addition to avai lable clinical findings. There were 13 men and seven women, with a mean age of 69 years. Five patients had documented Waldenstrom's macroglobulinemia (WM). Three architectural patterns were observed. Pattern A (seven of 20) s howed open sinuses, small follicles, and hemosiderosis; pattern B (four of 20) showed hyperplastic follicles; and pattern C (nine of 20) showed diffus e effacement. Epithelioid histiocytes were prominent in patterns B and C bu t absent in A. Cytologically, six of 20 were polymorphous with 10% to 40% t ransformed cells; 14 of 20 were lymphoplasmacytic. Five cases showed minor foci of monocytoid B cells. One case showed a composite histology of LLI an d small lymphocytic lymphoma. Amyloid was present in two cases. All cases w ere CD20 and/or CD79a immunoreactive, with two of 20 positive for CD43. Twe lve cases were kappa monoclonal and eight cases were lambda monoclonal. Twe lve of 17 cases that could be evaluated were positive for IgM and five were positive for IgG. All cases were negative for CD5 and CD23 with the except ion of the one case with a composite histology. Eleven of 20 patients with available follow-up died of disease (median, 48 months), and eight of 20 ar e alive with disease at a followup of 6 months to 2 years. LLI does appear to represent a distinct clinicopathologic entity even though it shows morph ologic heterogeneity and overlapping features with marginal zone B-cell lym phoma and small lymphocytic lymphoma. Recognition of LLI is important becau se the overall prognosis may be worse than for other types of small B-cell lymphomas.