The utility of CD20 and CD43 in subclassification of low-grade B-cell lymphoma on paraffin sections

To identify phenotypic differences among the low-grade lympho-proliferative disorders in paraffin-embedded tissue, we studied 49 cases. All 22 follicular small cleaved cell lymphomas (FSC) were CD43 negative and CD20 positive. In contrast, of 20 small lymphocytic lymphomas (SL), 90% were CD20 positive, 85% were CD43 positive, and 75% were positive for both. Of three lymphomas of intermediate differentiation (IDL), two were CD20 positive and two were CD43 positive. All four monocytoid B-cell lymphomas were positive for CD20 and 50% (two cases) were positive for CD43. Some 86% of 14 chronic lymphocytic leukemias (CLL) (on cytospins) were positive for CD43; all nine of the CLL studied for CD20 were positive and 89% (8/9) expressed both antibodies CD5 expression (on frozen sections or cytospin preparations) was compared to CD43 in 21 cases of SL and CLL. Some 77% were positive for both CD5 and CD20. All seven of the CD5-positive SL also expressed CD43. The antibody MT2 was also examined with the following results: FSC, 16/20 (80%) positive; SL, 18/19 (94%) positive; MBC, 3/3 positive; and ILL, 2/3 positive. All 56 cases tested were CD45RO (UCHL1) negative. We conclude that CD43 is expressed on most cases of low-grade lymphoproliferative disorders with the exception of FSC. Its pattern of expression seems similar to CD5; however, unlike CD5, CD43 can be studied in formalin-fixed tissue. MT2 is not helpful in distinguishing among these lesions.