VEGF-C and COX-2 expression in papillary thyroid cancer

In papillary thyroid cancer (PTC), age appears to be the most important single prognostic factor. Another characteristic feature is the lack of association between survival and lymph node metastases. Earlier, we found that expression of cyclooxygenase-2 (COX-2) is higher in older PTC patients, in agreement with the finding that older patients have a worse prognosis. Recent findings suggest that COX-2 can up-regulate vascular endothelial growth factor-C (VEGF-C) expression. Here, we investigated whether expression of VEGF-C differs between young and older PTC patients and whether expression of VEGF-C and COX-2 are correlated. Our retrospective study comprised 106 PTC patients selected by age: those under 35 or over 55 at diagnosis. Paraffin-embedded tissue samples were analysed by immunohistochemistry for VEGF-C protein expression. Furthermore, we investigated by quantitative RT-PCR and enzyme immunoassay the relationship between VEGF-C and COX-2 expression in papillary thyroid cancer cells (NPA cells). VEGF-C expression was significantly increased with age. In the tumours from older lymph node-positive (N1) patients, VEGF-C expression was significantly higher than in the tumours from young N1 patients. Moreover, all patients who died of cancer or who developed distant metastases were old, and most tumours from these patients (4 of 5) expressed VEGF-C and had had nodal metastases at the time of primary operation. Immunohistochemically, expression of COX-2 and VEGF-C correlated strongly. In cell culture, this correlation was not so clear, because the COX-2 selective inhibitor, NS-398, did not reduce VEGF-C expression. However, as both COX-2 and VEGF-C were induced by the tumour promoter phorbol 12-myristate 13-acetate (PMA), the same factors may control them both.