Significance of CD10 protein expression in the diagnostics of follicular lymphoma: A comparison of conventional immunohistochemistry with flow cytometry supported by the establishment of BCL2 and BCL6 rearrangements

Abstract Introduction Histopathological examination and immunohistochemistry (IHC) with a crucial role of CD10 expression remain a standard diagnostic tool in follicular lymphoma (FL). The results of IHC CD10 detection with different primary antibodies are not fully reproducible, but some reports show that flow cytometry (FCM) can be a reliable method of CD10 identification. Methods The aim of the study was to compare results of CD10 expression in FL by IHC and FCM including immunophenotypic features in the context of the BCL2 and BCL6 alterations. Results Out of 76 histopathologically diagnosed FL, a group of 25 cases had simultaneously FCM. Immunohistochemically 77.6% of cases were CD10‐positive with comparable and reproducible results to FCM. Differences between the FCM expression of CD5/CD10/CD11c/CD25/CD43 and BCL2 overexpression (BCL2(+) higher ) correlated with the BCL2 and BCL6 rearrangements (R) status. Lack of CD10 expression corresponded with the absence of BCL2 R and higher MUM1 expression by IHC results but had no clinical impact on the long‐time outcomes. Conclusions Immunohistochemistry staining is a comparable method to FCM assessment in the evaluation of CD10 expression and diagnosis of FL. Fine‐needle aspiration biopsy/FCM (FNAB/FCM) could be a useful tool for verifying FL diagnosis and CD10 detection. Despite its heterogeneity, FL has a characteristic immunophenotype. BCL2 R and BCL6 R FL cases differ mainly in levels of BCL2 and CD10 with CD43 co‐expression; BCL2(+) higher by FCM correlates with BCL2 R. Moreover, FNAB plays an important role in material provision for supportive karyotyping and BCL2 R, BCL6 R assessed by FISH.