MALDI-MSI analysis of cytological smears: The study of thyroid cancer

Fine needle aspiration (FNA) biopsies are the current gold-standard for the preoperative evaluation of thyroid nodules. However, a significant number of them (15–30%) are unable to be affirmatively diagnosed and are given an “indeterminate for malignancy” final report, meaning that the malignant nature of the thyroid nodule remains unknown and the recommended therapeutic approach is total thyroidectomy. Furthermore, cytomorphological evaluation of biopsies taken post-surgery indicates that approximately 80% of nodules within this group of patients are in fact benign, and the total thyroidectomy unwarranted. Therefore, the identification of new possible diagnostic targets that can assist in the preoperative diagnosis of thyroid tumors and reduce the number of unnecessary thyroidectomies is imperative. Matrix-Assisted Laser Desorption/Ionization (MALDI)—Mass Spectrometry Imaging (MSI) has the ability to provide very precise and localized information regarding protein expression in cytological specimens. This enables the detection of cell subpopulations based on their different protein profiles, even within regions that are indistinguishable at the microscopic level, and the feasibility of this approach to investigate FNA specimens has already been highlighted in a number of studies. Here, an overview about the sample preparation procedure for the MALDI-MSI analysis of ex vivo FNA biopsies is provided, highlighting how molecular imaging can be combined with traditional histology to generate protein signatures of the different thyroid lesions, and, ultimately, build classification models that can be potentially used to classify benign and malignant thyroid nodules from a molecular standpoint.