B cell associated monoclonal antibody L26 may occasionally label T cell lymphomas.

Monoclonal antibody L26 has been shown to be a very sensitive marker for B lymphocytes in formalin-fixed, paraffin-embedded tissue. Most studies have found that the antibody is also highly specific for B cells, although a few examples of L26-positive T cell lymphoma (TCL) have been reported. We have studied L26 reactivity in 50 TCLs (all previously extensively immunophenotyped on frozen sections) and found positive labelling in 4 cases (3 pleomorphic, medium and large cell type with surface membrane staining; 1 T-anaplastic large cell type with cytoplasmic staining). The finding that L26 may give surface labelling in occasional TCLs (particularly of the pleomorphic, medium and large cell type) indistinguishable from that seen in B cell lymphomas emphasises the importance of always using diagnostic MAbs in combination if the risk of misinterpretation of lymphoma cell lineage is to be minimised.