Fluorescence in situ hybridization analysis of single-cell trisomies for determination of clonality.

Conflicting data currently exist pertaining to the significance of single-cell trisomies found in a 20-cell cytogenetic analysis of hematologic malignancies. In order to determine the clonality of the numerical abnormalities found in these cases, we performed a retrospective study on a cohort of patients previously analyzed by GTG-banding at Rhode Island Hospital, from July 1, 1990 to November 30, 1996. Fluorescence in situ hybridization (FISH) was performed using chromosome enumeration probes on previously fixed bone marrow and, in some cases, peripheral blood slides from patients identified to have single-cell trisomies of selected chromosomes in 20-cell routine GTG-banded analyses. We seek to determine whether the single cell trisomies represent random nonclonal events or "the tip of an iceberg." The results of the present study indicate that a single unifying answer to the above question does not exist. While some cases are apparently random events as predicted by chance, other cases appear to represent "the tip of an iceberg." It is therefore important for cancer cytogeneticists to interpret the results of each patient on a case-by-case basis and to formulate the most optimal strategy for follow-up in the particular case under study.