Raman Spectroscopy Discloses Altered Molecular Profile in Thyroid Adenomas

Abstract

Follicular patterned nodules are sometimes complex to be classified due to ambiguous nuclear features and/or questionable capsular or vascular invasion. In this setting, there is a poor inter-observer concordance even among expert pathologists. Raman spectroscopy was recently used to separate benign and malignant thyroid nodules based on their molecular fingerprint; anyway, some histologically proved follicular adenomas were clustered as having a characteristic profile of malignant lesions. In this study, we analyzed five follicular thyroid adenomas with a malignant spectroscopic profile compared to five follicular adenomas with a benign Raman spectrum in order to assess possible molecular differences between the two groups. Morphological, immunohistochemical, and molecular analyses evidenced expression of malignancy-associated proteins in four out of five malignant clustered adenomas. The remaining malignant clustered adenoma showed a TSHR mutation previously associated with autonomously functioning follicular carcinomas. In conclusion, thyroid follicular adenomas are a group of morphologically benign neoplasms that may have altered the mutational or expression profile; cases of adenomas with altered immunophenotype are recognized as showing a profile associated with malignancy by Raman spectroscopy. This correlation warrants a more extensive evaluation and suggests a potential predictive value of spectroscopic assessment in recognizing characteristics associated with tumor progression in follicular thyroid neoplasms.

Keywords: Raman spectroscopy; follicular adenoma; follicular carcinoma; immunohistochemistry; molecular markers; mutational analysis; thyroid.

Figure 1

Agglomerative hierarchical clustering analysis (AHCA) dendrogram of the ten adenoma samples investigated. Notice that: 5 of them fall within the healthy cluster (labelled H/B, in red, A), while the others are spread among the three cancer categories, namely follicular carcinoma, labelled FC (blue, C), papillary carcinoma, labelled PTC (green, B)), and follicular variant of papillary carcinoma, labelled FV-PTC (brown, D). HB.txt, FC.txt, PTC.txt, and FV-PTC.txt indicate the reference spectrum for each category.

Figure 2

Five cases that dropped in the malignant Raman clusters: four of them show altered expression of immunohistochemical markers, although with different distribution on the samples. (+ positive reaction; - negative reaction)The cartoons on the right-hand panels model different patterns of markers expression.

Figure 3

Five cases that dropped in the benign Raman clusters: none of them show expression of proteins acquired during neoplastic transformation; two out of five show minimal loss of CD56 (see microscopic images) (+ positive reaction; - negative reaction). The cartoons on the right-hand panels model different patterns of markers expression.