Heterogeneity in the Distribution ofRET/PTCRearrangements within Individual Post-Chernobyl Papillary Thyroid Carcinomas

Abstract

The nuclear disaster that occurred in Chernobyl in 1986 offered the unique opportunity to study the molecular genetics of one human tumor type, papillary carcinoma of the thyroid gland, associated with a specific etiology. We have analyzed RET rearrangements in post-Chernobyl papillary thyroid carcinomas (n = 29), follicular thyroid adenomas (n = 2), and follicular thyroid carcinoma (n = 1) by interphase fluorescence in situ hybridization (FISH) analysis on paraffin-embedded tissue sections. Paraffin sections were microdissected before use to ensure that only tumor was present. Cell nuclei were scored for the presence of a split FISH signal (separated red and green signal) in addition to an overlapping signal. Only cells with either two overlapping signals or one split and one overlapping signal were counted to ensure that only complete cell nuclei had been scored. In total, 23 of 32 cases (72%) showed RET rearrangements diagnosed by FISH interphase analysis. In all cases, the tumors were composed of a mixture of cells with and without ret rearrangement on FISH. In some cases, this distribution was clearly nonrandom because clustering of rearranged cells was detected within the same tumor nodule. Accordingly, only 31% of the cases positive for rearrangement on FISH also scored positive using RT-PCR. These findings suggest that because RET/PTC rearrangements are not present in a majority of tumor cells, either a fraction of post-Chernobyl papillary thyroid tumors are of multiclonal origin, or ret rearrangement is a later, subclonal event.

Array CGH demonstrates characteristic aberration signatures in human papillary thyroid carcinomas governed by RET/PTC

“…An interesting finding of this study is the deletion of RET because its activated form, RET/PTC, is known as a marker of PTC. This apparent contradiction, being simultaneously present as an activated oncogene and affected by a deletion, can be explained by a distinct genetic heterogeneity in tumour tissues as already extensively reported for RET/PTC (Unger et al, 2004Ciampi and Nikiforov, 2007). We confirmed this genetic heterogeneity for RET/PTC by performing RET/PTC analysis at a single-cell level by FISH in this study (data not shown).…”

“…However, the identification of RET/PTC in other common thyroid tumour histotypes such as oncocytic adenomas and carcinomas (Cheung et al, 2000), and even in hyperplastic thyroid nodules (Ishizaka et al, 1991;Elisei et al, 2001) and Hashimoto's thyroiditis (Rhoden et al, 2006), seems to challenge the validity of RET/PTC as a tumour marker and its specificity for PTC. Moreover, it has been recently shown that the level of RET/PTC expression in papillary carcinoma is highly variable, suggesting that the distribution of RET/PTC within one tumour may not be homogenous (Rhoden et al, 2004;Unger et al, 2004). This is also supported by recent fluorescence in situ hybridization (FISH) studies by ourselves and others (Unger et al, 2004;Ciampi and Nikiforov, 2007).…”

“…Moreover, it has been recently shown that the level of RET/PTC expression in papillary carcinoma is highly variable, suggesting that the distribution of RET/PTC within one tumour may not be homogenous (Rhoden et al, 2004;Unger et al, 2004). This is also supported by recent fluorescence in situ hybridization (FISH) studies by ourselves and others (Unger et al, 2004;Ciampi and Nikiforov, 2007).…”

“…Hybridization of BAC clones to paraffin-embedded tissue sections of a representative PTC case carrying the respective alteration and detection of fluorescent signals were performed as described previously (Unger et al, 2004).…”

Diffuse sclerosing variant of papillary thyroid carcinoma: lack of BRAF mutation but occurrence of RET/PTC rearrangements

“…53,54 Using fluorescence in situ hybridization (FISH), Unger et al 53 revealed that within a single PTC, only a subset of tumour cells (not more than 46%) showed RET/PTC rearrangement beside areas completely lacking tumour cells with RET/PTC rearrangement. In contrast to these studies, Zhu et al 54 using FISH technique reported that the vast majority (50-86%) if not all tumour cells carried the rearrangement.…”