edullary thyroid carcinomas are aggressive neoplasias that metastasize very early to loco-regional lymph nodes, and tumors with a desmoplastic stromal reaction have a higher incidence of lymph node metastasis. In order to characterize the desmoplastic response in thyroid cancers, we evaluated the expression pattern of three molecular markers of activated fibroblasts/myofibroblasts, namely, fibroblast activation protein α (FAPα), tenascin-C (Tn-C), and α-smooth muscle actin (α-SMA), as well as the endothelial markers endoglyx-1, CD34 and CD31 in a series of 28 metastatic and non-metastatic medullary thyroid cancers. Immunohistochemical studies demonstrated that the three fibroblast activation markers (FAPα, Tn-C, α-SMA) are consistently expressed in the peritumoral and intratumoral stromal compartment of medullary thyroid carcinomas and expression of FAPα and Tn-C correlated with the degree of desmoplasia determined histologically (p=0.001 for FAPα and p<0.001 for Tn-C). Moreover, the extent of desmoplasia as well as the expression of FAPα and Tn-C correlated with the presence of lymph node (LN) metastases (p=0.002, p=0.005 and p=0.002, respectively). No correlation was found between the microvessel density (neoangiogenesis) in the tumor stroma, assessed with the endoglyx-1, CD34 and CD31 markers, and the degree of desmoplasia or incidence of LN metastases. Using a bioinformatics-based search of the BioExpress™ database we found in a series of 48 thyroid cancers a significant correlation between FAPα RNA expression and incidence of LN metastases also in papillary cancers. These findings suggest that the link between specific molecular markers of tumor stromal reaction and locoregional metastasis extends from medullary to other thyroid cancer types.

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