DIFFERENCES IN CELL LINEAGE INVOLVEMENT BETWEEN MDS-AML AND DE-NOVO AML STUDIED BY FLUORESCENCE IN-SITU HYBRIDIZATION IN COMBINATION WITH MORPHOLOGY

We have employed fluorescence in situ hybridization (FISH) in combinat ion with standard morphology (MGG/FISH) to identify the clonal involve ment of different bone marrow cell lineages in 20 AML patients (14 MDS -AML, 6 de novo AML). Even though the number of cells belonging to the abnormal clone varied between individual cases, the percentage of clo nal blasts was similar in MDS-AML and de novo AML patients. The erythr opoietic cells appeared to be part of the abnormal clone in 13 of 14 p atients with MDS-AML, but only in 1 of 6 with de novo AML. Similarly, clonal granulocytes were detected in 13 of 14 patients with MDS-AML, c ompared to 2 of 6 with de novo AML. Lymphocytes consistently displayed normal, diploid karyotype. The results suggest that it is possible to distinguish between MDS-AML and de novo AML by the use of MGG/FISH; i n de novo AML the abnormal chromosomal clone is generally confined to the immature myeloid cells, while in MDS-AML mature granulocytes and e rythroid cells are of clonal origin. It is, however, not possible to c onclude that MDS-AML is a ''multipotent'' type of leukaemia, since it cannot be ruled out that the chromosomally aberrant erythroid cells an d granulocytes represent surviving cells from the original MDS clone.