Determination of frequency of the main cytogenetic subgroups in benign thyroid lesions by interphase fluorescence in situ hybridization

In the past, conventional cytogenetics (CC) of benign thyroid lesions led to the identification of three main cytogenetically aberrant subgroups, characterized by trisomy 7, structural aberrations involving either chromosomal region 19q13.4 or 2p21, respectively. However, these subgroups were previously identified mainly by CC and with exception for trisomy 7 not by interphase FISH (I-FISH). Furthermore, although I-FISH has been performed in the past on benign as well as malignant thyroid lesions, this was rarely done in combination with CC. The aim of this work was the analysis of benign thyroid lesions with both CC and I-FISH on touch-preparations using a multi-target, triple-color FISH assay as well as dual-color, break-apart probes for detection of these cytogenetic subgroups. First, I-FISH analysis yielded results in nearly 97.5% of 161 cases analyzed, while in comparison CC was successful only in 82%. Interestingly, I-FISH was shown to detect a higher rate of cytogenetic aberrations than CC. This suggests that cell populations belonging to any of the three cytogenetically aberrant subgroups are more frequent in benign thyroid lesions than previously assumed. In summary, I-FISH using touch preparations of benign thyroid lesions seems to be a favorable method for cytogenetic sub-typing of thyroid lesions.