Comparison between interphase and metaphase cytogenetics in detecting chromosome 7 defects in hematological neoplasias.

Monosomy 7 (-7) is one of the most common chromosomal abnormalities found in the leukemic cells of patients with acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS). Because patients with -7 have a poor prognosis, their identification is important for treatment planning. Conventionally, -7 is detected by the G-banding technique. This study examines the use of fluorescent in situ hybridization (FISH) methodology to detect -7 cells in interphase nuclei and metaphase chromosomes. Fifteen AML or MDS patients whose leukemic cells were found to have -7 by G-banding at disease presentation were studied. In 13 of these patients, -7 could be detected in interphase by FISH using a chromosome 7-specific centromeric DNA probe. The two patients whose leukemic cells were not detectable by interphase FISH had -7 and t(1q;7p), which were detectable by FISH in metaphase using a chromosome 7-specific painting probe. Metaphase FISH was particularly useful in further defining chromosome 7 defects in cells that contained aberrant or marker chromosomes. For example, in 6 patients, chromosome 7 sequences were detectable in aberrant or marker chromosomes by metaphase FISH, but not by G-banding. These results suggest that metaphase FISH is an important adjunct to conventional cytogenetic methods for defining chromosome 7 abnormalities in AML and MDS patients. Furthermore, interphase FISH is useful for follow-up studies in patients who are found informative for the FISH study at presentation.