Classification of acute myeloid leukaemia in trephine biopsies with special reference to lactoferrin.

In spite of advances in immunohistochemical techniques, the histological subclassification of acute myeloid leukaemia (AML) in bone marrow biopsy has remained difficult. In particular, the translation of the diagnostic criteria of the French-American-British (FAB) cooperative group as primarily defined by bone marrow cytology into histology poses considerable problems. In this study, we investigated the expression of lactoferrin (LF) in various subtypes of AML and studied the usefulness of its immunohistochemical detection combined with a panel of antibodies directed against myeloperoxidase (MPOX), lysozyme (LYS), CD34 and naphthol-AS-D-chloroacetate esterase (NACE) staining in solving this problem. Trephine biopsies of 52 cases of AML were selected for histological evaluation in comparison to bone marrow aspirates classified according to FAB (M1 n = 10, M2 n = 7, M3 n = 11, M4 n = 13 and M5 n = 11). The results obtained confirmed the specificity of LF as a marker for secondary granules in neutrophilic myeloid cells and as a tool to subclassify AML. Its parallel application with (immuno-)staining for MPOX, LYS and NACE has allowed the identification of M1, M3, M5 cases, where there LF is lacking. Typically M2 is characterized by a subpopulation of LF-positive cells which tend to display a myelocytic differentiation. However, M4 shows a heterogeneous expression pattern of LF: M4a may be defined as more immature variant without LF expression while in M4b a more mature myeloid subpopulation stains positive for LF.