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.