Purpose: To prospectively compare cytogenetic and molecular cytogenetic analysis for the detection of the most relevant chromosome abnormalities in a large series of patients with acute myeloid leukemia (AML).

Patients and Methods: Two hundred forty consecu-tive adult patients with AML entered onto the multicenter treatment trial AML HD93 were studied. Chromosome banding and fluorescence in situ hybridization (FISH) applying a comprehensive set of genomic DNA probes were performed in a single reference laboratory.

Results: Two cases of inv (16), three cases of t (11q23), and three cases of t (8; 21) var were only detected by molecular cytogenetics. By FISH, aberrations were identified in three cases with normal karyotypes: inv (16), Y (in a patient with low metaphase yield on chromosome banding) and a 12p microdeletion. Additional aneuploidies, in particular 8q and 11q, were diagnosed by FISH; however, virtually all these aberrations occurred in patients with complex karyotypes or as an additional abnormality in leukemias with an AML-specific translocation. Finally, aberrations were detected by FISH in eight of 14 patients with no assessable metaphases.

Conclusion: In most cases of AML, conventional cy-togenetic study reliably detects chromosomal abnormalities, and this method should not be replaced by FISH. FISH should be used as a complementary method for the detection of more subtle abnormalities, such as inv (16) and t (11q23), in all patients with newly diagnosed AML and for suspected t (8; 21) var. Furthermore, molecular cytogenetics using this comprehensive set of DNA probes provides a valuable diagnostic tool for patients with poor chromosome morphology, low or no yields of metaphase cells, or both.