Tissue imprints or primary cultures: which strategy to use to study cytogenetic clonality?

Touch preparations or imprints have been extensively used in cytogenetics to avoid primary cultures, especially when studying solid tumors which are hard to grow in vitro. Interphase nuclei studies by FISH have been validated in several sample types; however, to our knowledge, a comparison between both methods when studying clonality has not yet been published. We have performed a comparative FISH study between touch preparations and cultured cells to assess their reliability when studying the aneuploidy of chromosome Y in mosaicism. Our results in 23 samples indicate that aneuploidy of chromosome Y assessed in cells from tissue cultures versus cells obtained from touch preparations from seminal vesicles of patients with prostate cancer is not comparable. The percentage of aneuploid cells is higher in cultured cells. Attention, therefore, must be paid not to overestimating or underestimating the number of aneuploid cells detected when using interphase FISH studies, especially in solid tumors where clonality is very frequent. Also, according to our results, it is reasonable to extrapolate that when performing interphase nuclei studies in paraffin sections or tissue microarray, and therefore underestimations of aneuploidy could be reported. This might be of special relevance if the aneuploidy detected correlates with the tumor progression or might be used as a prognostic factor.