Immunohistochemical Detection of Hairy Cell Leukemia in Paraffin Sections: The Role of Pax5 and CD103 Double Staining to Improve Specificity and Sensitivity.

CONTEXT: - In hematopathology practice, abnormal expression of CD103 on B cells is detected by flow cytometry in hairy cell leukemia (HCL) and, in combination with other phenotypic and morphologic findings, provides diagnostic specificity and sensitivity. Immunostaining on paraffin sections makes it possible to perform immunophenotyping in situ. However, normal bone marrow contains CD103-positive cells, which are not B cells, making it difficult to be certain about low-level involvement by HCL. OBJECTIVE: - To develop dual immunostaining for confirmation that CD103 is expressed in B cells, which may be highly desirable in assessing low-level involvement by HCL. DESIGN: - We developed a dual immunostaining approach using a B-cell marker, Pax5, expressed in the nucleus, in combination with a membrane marker, CD103. RESULTS: - We analyzed 6 HCLs, 7 marginal zone lymphomas, 12 lymphoplasmacytic lymphomas, 7 follicular lymphomas, 5 chronic lymphocytic leukemias, 5 mantle cell lymphomas, 1 multiple myeloma (lymphocytic variant), and 3 bone marrows not involved by any B-cell neoplasm. Our dual staining approach confirmed that only the neoplastic cells of HCL were positive for both CD103 and Pax5. CONCLUSIONS: - This dual-staining method is particularly helpful in cases with low-level involvement by HCL and can be used for determining minimal residual disease after treatment.

Extracavitary KSHV-associated large B-Cell lymphoma: a distinct entity or a subtype of primary effusion lymphoma? Study of 9 cases and review of an additional 43 cases.

Primary effusion lymphoma (PEL) is a rare form of aggressive B-cell lymphoma in HIV patients, which typically presents with lymphomatous effusions in the body cavities without forming mass lesions. PEL is associated with Kaposi sarcoma-associated herpesvirus (KSHV) (also called human herpesvirus-8) with distinct clinical and pathologic features. Rare cases of KSHV-associated large B-cell lymphoma (KSHV-LBL) have been observed in the lymph nodes or extranodal sites without lymphomatous effusions during the course of disease. KSHV-LBL is generally similar to classic PEL on the basis of the clinical presentation (HIV(+) male), morphology (immunoblastic, plasmablastic, or anaplastic), immunophenotype (CD45(+), CD20(-), CD79a(-), CD30(+), CD138(+), and EMA(+)), presence of Epstein-Barr virus infection, and clonal immunoglobulin gene rearrangements. However, it is not clear whether KSHV-LBL is a distinct entity or represents part of the spectrum of classic PEL; in particular, there is no consensus diagnostic term for KSHV-LBL. In this study, we investigated the clinicopathologic features of 9 cases of KSHV-LBL from our files. An additional 43 such cases and 84 cases of classic PEL from the English literature were reviewed and compared with each other. In contrast to the classic PEL, KSHV-LBL had a very significant lower expression of CD45 (74% vs. 94%, P=0.004) but significant higher expression of CD20 (17% vs. 5%, P=0.04) and CD138 (70% vs. 38%, P=0.05). KSHV-LBL also had slightly higher positivity of CD79a (23% vs. 5%, P=0.13) and immunoglobulin light chain expression, although the difference was not statistically significant [κ chain (12% vs. 0%) and λ chain (31% vs. 21%)]. The expressions of EMA and CD30 were slightly lower in KSHV-LBL compared with those observed in PEL (57% vs. 75% and 63% vs. 76%, respectively). Interestingly, 29% (10/34) of cases of KSHV-LBL revealed aberrant CD3 expression, which may mislead to a diagnosis of T-cell lymphoma, particularly anaplastic large cell lymphoma in combination with the anaplastic morphology and expression of CD30 and EMA. Although KSHV-LBL shows different clinical presentations and some variations in immunophenotype from classic PEL, it is still uncertain, on the basis of our findings, whether it is justifiable to separate them as 2 distinct entities. Nevertheless, we feel it is necessary to have a consensus diagnostic term, and we recommend a tentative one as "KSHV-associated large B-cell lymphoma (KSHV-LBL)" to replace many different names previously used.