Background: Human papillary thyroid carcinoma (PTC) is often associated with Hashimoto's thyroiditis (HT); their coexistence improves PTC prognosis. Osteopontin, a secreted glycoprotein, plays a role in cell survival, immunity, and tumor progression, its expression being associated with a poor prognosis and metastasis in several malignancies. Osteopontin overexpression correlates with aggressive clinicopathological features in PTC. Lymph node metastases and large tumor size positively correlate with osteopontin positivity. This study aimed to: (1) confirm osteopontin overexpression in human PTC samples; (2) compare osteopontin expression levels in PTC cases with and without HT; and (3) identify correlations between tumor aggressiveness and osteopontin expression levels.
Materials and methods: Plasma osteopontin was assessed in 45 patients with PTC, 22 patients with PTC and HT, and 24 healthy controls by enzyme-linked immunosorbent assay. Thyroid tissue osteopontin mRNA and protein levels were analyzed by reverse transcription-polymerase chain reaction and Western blotting, respectively.
Results: Plasma osteopontin levels were significantly higher in PTC patients than in healthy controls. Plasma osteopontin, tissue osteopontin mRNA, and tissue osteopontin protein levels were significantly lower in patients with PTC and HT than in those with PTC alone. In advanced disease stage cases, osteopontin mRNA and protein expression levels were lower in patients with PTC and HT than in those with PTC alone. However, the osteopontin expression level was not significantly associated with the TNM stage.
Conclusions: Plasma osteopontin, tissue osteopontin mRNA, and tissue osteopontin protein levels were significantly lower in patients with PTC and HT than in those with PTC alone, suggesting that HT attenuates PTC aggressiveness through negative regulation of osteopontin expression.