Most experimental work addressing cyclooxygenase-2 (COX-2) inhibitor has focused on suppressing hematogenic spread. Little is known about the mechanism by which this inhibitor can also block lymphatic metastasis. Here, the effects of COX-2 inhibitor on vascular endothelial growth factor-C (VEGF-C) expression, lymphangiogenesis and lymph node metastasis were investigated. Utilizing the highly metastatic human lung adenocarcinoma cell line Anip973 and its parental line AGZY83-a, which has a low metastatic capacity, we found elevated VEGF-C and COX-2 immunoreactivity in Anip973 cells compared with AGZY83-a cells. Celecoxib down-regulated expression of VEGF-C mRNA and protein in Anip973 cells while PGE(2) up-regulated expression of VEGF-C mRNA and protein in AGZY83-a cells in a concentration-dependent manner. The expression of COX-2 and VEGF-C was significantly increased in xenografted Anip973 tumors compared with AGZY83-a tumors. The Anip973 tumors showed more lymphatic vessels and lymph node metastasis than the AGZY83-a tumors. In vivo, celecoxib decreased VEGF-C expression in Anip973 tumor-treated mice to a similar level to that in the AGZY83-a tumor-treated mice. Consistent with this decrease in VEGF-C expression, the density of lymphatic vessels and lymph node metastasis in Anip973 tumor-treated mice were suppressed to approximately that found in the AGZY83-a tumor-treated ones. Taken together, our results suggest that the differential expression of COX-2 and VEGF-C might help explain the different metastasis phenotype of lung adenocarcinoma cancer, and that COX-2 inhibitor mediates VEGF-C to block lymphangiogenesis and lymph node metastasis. Thus, COX-2 may be a potential therapeutic target for blocking lymph node metastasis in lung adenocarcinoma.