Immunophenotype

The neoplastic cells in cHL are almost always positive for CD30,23 24 and a large percentage of cases coexpress CD15 (70-80%)24'25 and PAX5 (up to 90%) (Figure 71.1).26'27 CHL is usually negative for CD45 and J-chain. CD20 may be found in a subset of cases but is usually present on only a minority of the neoplastic cells and expressed with variable intensity. The finding of strong CD20 expression on a large percentage of Reed-Sternberg-like cells suggests the diagnosis of a B-cell lymphoma, such as T-cell rich large B-cell lym-phoma.19 The B-cell transcription factors OCT-2 and/or BOB.1 are characteristically absent.9 Occasionally, other B-cell antigens such as CD79a may be present. Some cases may show aberrant expression of T-cell antigens, but the finding of multiple T-cell antigens should raise the possibility of a T-cell neoplasm, such as anaplastic large cell lymphoma.

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