Is there still a point for classical cytogenetic banding analysis in the diagnostic work-up of specimens suspicious for lymphoma?

In this issue of Leukemia and Lymphoma, Dunphy and Tang [1] present data on the conventional cytogenetic analysis in 261 specimens referred to a single institution for suspicion of lymphoma. In this series, banding analysis of the specimens after shortterm culture was part of the routine work-up. This article, aside from its interesting data, tackles the question if, in the era of molecular diagnostics, classical banding analysis still has its place in diagnosis. Why still do classical cytogenetics requiring at least short-term culturing of viable tumor cells? Fluorescence in situ hybridization (FISH) can nowadays be reliably performed on formalin-fixed paraffin-embedded (FFPE) tissues [2], and is even more sensitive in the detection of chromosomal aberrations than classical cytogenetics. Comparative genomic hybridization (CGH) can also be performed on FFPE material. Moreover, the resolution of CGH has been significantly increased technically by applying microarray platforms [3], which even more enhance the detection threshold of small chromosomal imbalances. Thus, FISH and CGH techniques are able to overcome the fundamental shortcoming of classical banding analysis which is the need for viable native material with the possibility of extracting cells that have retained their ability to divide. One could therefore argue that the requirement of viable cells is a severe argument against the performance of cytogenetic studies in larger, controlled studies which, due to their multi-institutional design, usually lack access to fresh material. What is the point then? CGH studies, including matrix-based approaches, can only yield data on numerical imbalances in the genome of the tumor cells, i.e., losses or gains of chromosomal material. Thus, balanced chromosomal translocations cannot be captured by this approach. As for the FISH approach, two points can be made. The first point is that you can only detect what you are looking for: what you see is what you get. This means that the probe selection has to be restricted to one or a few chromosomal regions or breakpoints of interest, while other alterations in the genome are easily missed. This issue is addressed when experienced cytogeneticists humorously quote that ‘‘FISH analysis is something for people who can count up to three, but not more’’ given the fact that in banding analysis, knowledge of around 200 – 300 bands in the karyotype is needed for evaluation. In other words, classical karyotyping is the only means, at least at the level of the karyotype, by which an unsupervised overview of genetic changes in a cell can be obtained. This fact is nicely underlined in the present paper, in which conventional cytogenetics was also performed in specimens designated as reactive by histomorphological analysis [1]: in this series, 5 of 78 cases demonstrated karyotypic alterations despite of the morphological diagnosis of a reactive process, thus suggesting an underlying neoplastic disease. The second important point is quantitative in nature. For CGH analysis, a given aberration has to be present in 450% of the tumor cells, thus limiting the exploitation of the method in routine settings. Even though the detection limit using FISH is much lower (usually around 5 – 10%), a positive result in a range of 5% of the counted cells in a diagnostic specimen is ignored or remains in a diagnostic grey zone. In contrast, the detection of a known recurring translocation in a single cell in classical banding analysis (regardless of the number of normal metaphases encountered) will alert high suspicion,