Genetic heterogeneity of benign thyroid lesions. Static and flow cytometry, karyotyping and in situ hybridization analysis.

The present series includes 75 thyroid lesions (38 goiters, 30 adenomas, 3 follicullo-papillary encapsulated carcinomas and 4 normal thyroid) that were studied by static and flow cytometry. Four cases were also analyzed by in situ hybridization (centromeric probes for chromosomes 1 and 17) and 10 cases by G-banding cytogenetics. Results demonstrate a polymorphism and genetic instability in the thyroid tissue that may be related to the spontaneous polyploidization of their cells. The most consistent finding in cytometry was the presence of two clones associated with clinical or histological hyperactivity (46% versus 23% in non-functioning cases; chi2 distribution with a p < 0.05). Chromosomal anomalies were detected in two out of 10 cases: 46, XX, t(5,19) in 87% of cells of a diffuse hyperplastic goiter and 49, XX, +7, +17, +22 in 19% of cells of thyroiditis case. Finally, the in situ hybridization technique showed hidden trisomies of clonal origin in all of the cases studied. Evaluation of clonal trisomies by the in situ hybridization technique using the confidence interval of a binomial distribution is discussed.