In this issue of Endocrinology and Metabolism, Kwon et al. [5] evaluated the serum levels of two important adipokines, adiponectin and progranulin, in patients with PTC. They included 131 patients with PTC and 26 patients with confirmed benign thyroid nodules after thyroid surgery. The median level of serum adiponectin was 5.4 and 6.3 μg/mL in the PTC group and the benign nodule group, respectively. However, this difference was not statistically significant. In patients with PTC, serum adiponectin levels were not associated with clinicopathological parameters, including primary tumor size, cervical lymph node metastasis, extrathyroidal extension, and multifocality. These results on serum adiponectin levels in PTC patients are consistent with those of a previous study that evaluated serum adiponectin levels and the expression of its receptor in patients with PTC [6]. That study suggested that adiponectin receptor expression in tumor tissue, but not serum adiponectin levels, played an important role. A significant negative correlation was found between adiponectin receptor expression in tumor tissue and poorer pathological parameters, including multifocality, extrathyroidal extension, and advanced tumor-node-metastasis (TNM) staging [7]. These findings suggest that serum adiponectin levels per se are not an important factor explaining the potential mechanism through which obesity influences the carcinogenesis of PTC.

Kwon et al. [5] also evaluated the serum levels of progranulin, an adipokine implicated in diverse biological processes in embryogenesis, inflammation, insulin resistance, and carcinogenesis [8]. This is the first study to report a potential role of progranulin in thyroid carcinogenesis. The median serum progranulin level was 106.1 and 101.5 ng/mL in the PTC group and benign nodule group, respectively. The median progranulin level was significantly higher in patients with PTC greater than 1 cm than in those with micro-PTC. The proportion of patients with microscopic and gross extrathyroidal extension significantly increased with serum progranulin quartiles. These findings suggested that progranulin, a cysteine-rich secretory protein, may be a potential biomarker and therapeutic target of PTC. Progranulin is known to be as a growth factor implicated in tumorigenesis and a poor prognostic marker in breast cancer, non-small cell lung cancer, astrocytoma, glioblastoma, cervical cancer, and biliary tract cancers [8]. However, the mechanism of action through which progranulin contributes to carcinogenesis is unclear because the signaling receptor is still elusive. Recently, several candidate receptors such as sortilin, tumor necrosis factor receptor, and ephrin type-A receptor have emerged as potential links involved in the action of progranulin [9,10]. The potential association of progranulin upregulation with poorer pathological parameters of PTC might facilitate further research into the possible value of progranulin as a biomarker and therapeutic target.