OBJECTIVETo study the value of loss of CD10 expression in the diagnosis and differential diagnosis of follicular lymphoma (FL).

METHODSOne hundred and twenty-six cases of FL and 31 cases of reactive follicular hyperplasia (RFH) were studied with routine microscopy and immunohistochemistry.

RESULTSLoss of CD10 expression was observed in 37 cases (29.4%) of FL. Three patterns of CD10 loss were demonstrated, as follows: diffuse CD10 loss in all of the neoplastic follicles (33/37, 89%), CD10 loss in most follicles (3/37, 8%) and CD10 loss in only a few follicles (1/37, 3%). In general, loss of CD10 was frequently seen in higher-grade FL. Morphologically, the cases with CD10 loss showed follicular architecture. The neoplastic follicles in high-grade FL were of various sizes and showed irregular margins, while those in low-grade FL were relatively uniform in size with regular margin. Sometimes, the CD10-negative FL cells contained a clear cytoplasm, mimicking monocytoid B cells. On the other hand, CD10 expression was found in all of the 31 cases of RFH studied, with the exception of occasional individual or regressed follicles.

CONCLUSIONSThe expression of CD10 differs in FL and RFH. Loss of CD10 expression is seen mainly in FL. It is thus considered as a valuable parameter in differentiating between FL and RFH.