## 1 Introduction  
Thyroid tumors are the most frequent endocrine malignancies and their incidence is steadily increasing [1]. They are divided into epithelial and non-epithelial tumors. Follicular neoplasms of the thyroid gland include benign follicular adenoma (FA) and follicular carcinoma (FC) [2]. FA is the most common benign thyroid tumor and occurs in follicular cells. Macroscopically, it may appear as a single nodule, whose diameter can vary from a few millimetres to a few centimetres, surrounded by a single capsule. Microscopically, it is characterized by the proliferation of many follicles surrounded by a capsule and, depending on their size the adenomas can be sorted into normofollicular, microfollicular, macrofollicular, and solid-tribecular.  
Among thyroid carcinomas, FC is the second most common epithelial tumor after papillary carcinoma, occurring late in life, with the fifth and sixth decades being the most affected, and is more aggressive than papillary carcinoma [3]. Macroscopically it appears as a thyroid nodule of variable diameter and may or may not possess a capsule. Microscopically, FC consists of a proliferation of follicles, similarly to FA, but the neoplastic follicles invade the tumor capsule when present, penetrating into blood vessels and/or the adjacent normal thyroid tissue, a feature that can only be appreciated with histological but not with cytological techniques [4].  
Immunohistochemical analysis does not usually allow the differentiation between benign and malignant lesions and, as a consequence, the majority of patients with these lesions are referred to surgery without a precise diagnosis. For this reason, it is necessary to improve the preoperative diagnosis also because no clinical, radiological, or laboratory test currently available is sufficiently sensitive and specific to distinguish benign from malignant follicular lesions detected by fine-needle aspiration [5].  
Molecular chaperones are the main components of the chaperoning system with canonical and non-canonical functions [6; 7]. The former functions pertain to maintenance of protein homeostasis and include assisting in the: folding of nascent polypeptides as soon as they emerge from the ribosome and until they reach their native and biologically active tridimensional structure; prevention of protein misfolding and aggregation; translocation of proteins from one cell compartment to another; and driving damaged or unnecessary proteins toward degradation [8; 9; 10; 11; 12].  
Many chaperones are heat shock proteins (Hsp) but although not all Hsp are chaperones the terms molecular chaperone (or chaperone in short) and Hsp are used as synonyms. Chaperones are classified according to molecular weight [7] and designated variously, which causes confusion, and because of this, attempts at nomenclature standardization have been made [13].  
Although chaperones are considered essentially cytoprotective, it is now known that they can also be pathogenic if abnormal in structure, or location, or quantity, causing diseases named chaperopathies, including several types of cancer [7; 14].  
Some chaperones are increased in various cancers with the magnitude of the increase being closely associated with prognosis and with resistance to anticancer therapy, the former being worse and the latter being higher as the chaperones increase is bigger [15; 16].  
There are few data in the literature on the role of Hsp in thyroid cancer, for example Hsp27 was increased in anaplastic carcinoma [17], and in papillary carcinoma, in which it was induced by 17 \(\beta\)-estradiol, which facilitates proliferation and confers resistance to apoptosis [18]. In this study, we performed immunomodophilological analysis on samples of FA and FC to evaluate, for the first time to our knowledge, the tissue levels of Hsp27, Hsp60, Hsp70, and Hsp90. We focused on these chaperones based on the fact that they are implicated in chaperopathies, including carcinogenesis [15; 19].