PHENOTYPIC CHANGES IN ACUTE MYELOID-LEUKEMIA - IMPLICATIONS IN THE DETECTION OF MINIMAL RESIDUAL DISEASE

Aim-To explore the role of phenotypic changes as possible limiting fac tors in the immunological detection of minimal residual disease in pat ients with acute myeloid leukaemia (AML). Methods-20 relapses were eva luated, with special attention to changes in the criteria used for the definition of a phenotype as ''aberrant''. In all cases the same mono clonal antibody and fluorochrome were used at diagnosis and in relapse . Results-Six out of the 16 patients showed aberrant phenotypes at dia gnosis. At relapse, no changes in the aberrant phenotypes were detecte d in most of the patients; nevertheless, in two of the four patients w ith asynchronous antigen expression this aberration disappeared at rel apse. At diagnosis in both cases there were already small blast cell s ubpopulations showing the phenotype of leukaemic cells at relapse. Ten out of the 16 cases analysed showed significant changes in the expres sion of at least one of the markers analysed. Conclusions-At relapse i n AML the ''leukaemic phenotypes'' usually remained unaltered, while o ther phenotypic features-not relevant for distinguishing leukaemic bla st cells among normal progenitors-changed frequently; however, they we re not a major limitation in the immunological detection of minimal re sidual disease.