DIFFERENTIATION OF REACTIVE FROM NEOPLASTIC SMALL-CELL LYMPHOID AGGREGATES IN PARAFFIN-EMBEDDED MARROW PARTICLE PREPARATIONS USING L-26 (CD20) AND UCHL-1 (CD45RO) MONOCLONAL-ANTIBODIES

The pathologic findings in 1,390 consecutive patients who had bone marrow examinations at Nashville Veterans Administration Hospital from 1977 through 1979 were reviewed. Seventy-three patients who did not meet diagnostic criteria for a small-cell lymphoid neoplasm (SCLN) and 11 patients with SCLN had, on marrow particle preparations: (1) at least three lymphoid aggregates and (2) suitable material available for immunoperoxidase studies with monoclonal antibodies UCHL-1 (CD45RO, pan T cell) and L-26 (CD20, pan B cell). Staining with UCHL-1 was difficult to interpret due to high background positivity in myeloid elements. With L-26, three distinct patterns of lymphocyte marking were identified within aggregates: (1) homogeneous-uniform marking of almost all lymphocytes; (2) mixed-even distribution of marking and nonmarking lymphocytes; (3) and focal homogeneous-collections of uniformly marking lymphocytes either surrounding or surrounded by nonmarking lymphocytes. A homogeneous marking pattern was the predominant pattern in 8 of 11 patients (73%) with SCLN. Only 6 of 73 patients without overt SCLN marked in a homogeneous pattern, and these were always associated with aggregates with other staining patterns. All patients with apparently non-neoplastic lymphoid infiltrates had mixed (67 of 73) or focal homogeneous (32 of 73) patterns of aggregate marking, whereas only 5 of 11 patients (45%) with extramarrow SCLN had aggregates with these patterns. The size and number of aggregates with a homogeneous marking pattern further helped discriminate between the patients with SCLN and those with apparently non-neoplastic lymphoid aggregates. These findings suggest that a homogeneous pattern of lymphoid aggregate staining with 1,26 is more common in patients with SCLN than in those patients with lymphoid aggregates and no evidence of neoplasia. Paraffin immunoperoxidase staining with L-26 may be a helpful adjunct to histopathologic examination in evaluating marrow lymphoid aggregates.