Place de la cytométrie en flux dans le diagnostic et le suivi des syndromes lymphoprolifératifs B

The considerable expansion of flow cytometry allows a rapid and reliable evaluation of cellular subsets in blood and bone marrow samples as well as in biological fluids (ascitic, pleural and cerebrospinal) even if they are in weak quantities. Thus, flow cytometry represents a major step in the diagnosis and the follow up of the majority of malignant hemopathies, in particular in B lymphoproliferative disorders. The detection of a monotypic population, a phenotypic gap, a lack of expression of a physiological marker or the expression of an aberrant marker, allow to suspect the abnormal feature of the sample. Based on immunophenotype, it is possible to determine the cellular lineage which the lymphoma population originates from, the classification of the pathology, the evaluation of the prognosis and the detection of the minimal residual disease (MRD). Among the B lymphoproliferative disorders, the most frequent and better characterized by flow cytometry is the chronic lymphocytic leukemia, the diagnosis of which is performed by the establishment of the Matutes/ Moreau score based on the expression of 5 markers. In atypical cases, the differential diagnosis with other types of lymphoproliferative syndromes may be difficult. The combination of some selected antigens allows to suspect or to diagnose other B-cell disorders such as mantle cell lymphoma, marginal zone lymphoma, follicular lymphoma, hairy cell leukemia, B prolymphocytic leukemia and lymphoplasmacytic lymphoma. In addition, the MRD quantification brings additional significant information in the evaluation of the treatment response and in the prediction of clinical outcome. The detection of MRD by flow cytometry, principally developed in CLL, should be currently restricted to clinical trials. However, after the standardization of the methods, we can hypothesize that the guidelines for these lymphomas will be reconsidered in order to integrate the MRD quantification.