Small lymphocytic lymphoma (SLL), mantle cell lymphoma (MCL), and SLL plasmacytoid (SLLP) are malignant neoplasms of small B cells that may have overlapping cytologic features. Entities such as SLL with irregular nuclear contours may pose additional diagnostic difficulties. We investigated the utility of flowHistologically, small lymphocytic lymphoma (SLL), mantle cell lymphoma (MCL), and SLL plasmacytoid (SLLP) are lymphomas composed of small lymphocytes. Distinguishing these lymphomas from each other on histologic grounds can be difficult. Particularly when SLL is composed of lymphocytes with irregular nuclear contours, it may be difficult to distinguish SLL from MCL. Yet this distinction is important clinically inasmuch as MCL has a shorter median survival than SLL or SLLP, and it is treated more aggressively than SLL or SLLP.1 Furthermore, it is important to distinguish SLL from SLLP because SLLP is often associated with macroglobulinemia and its hyperviscosity complications.
2Immunophenotypic characterization of these disorders by flow cytometry and immunohistochemistry has been shown to be a useful adjunct to their histologic classification. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] CD23 is a B-cell activation antigen that functions in IgEmediated presentation to T cells 17 and prevents apoptosis of B cells in germinal centers. 18 Recently, assessment of CD23 expression by flow cytometry has been found to be useful in distinguishing SLL from MCL 56 and discriminating SLL from SLLP. 6 By both flow cytometry and immunohistochemistry, CD23 has tended to be present in SLL, absent in MCL) 4,7,10,1U3,19 a n d a b s e n t i n SLLP. 478 ' 13 However, there have been reports of CD23 expression in a majority of SLLP" or MCL cases. 20 The use of anti-CD23 by immunohistochemistry has been successful with frozen section material. Recently, two published studies reported success with anti-CD23 in paraffin-embedded material.
7,21Our objectives in this study were 3-fold: investigate the utility of immunohistochemical detection of CD23 expression in paraffin-embedded material to aid in the distinction of SLL from MCL and SLL from SLLP; investigate whether a battery of other immunophenotypic markers can help in making these distinctions by immunohistochemical and flow 5 8 2