Tissue factor pathway inhibitor‑2 (TFPI‑2) is a promising candidate as a serum biomarker of ovarian clear cell carcinoma (OCCC), a lethal histological subtype of epithelial ovarian cancer (EOC). TFPI‑2 is a secreted serine protease inhibitor that suppresses cancer progression through the inhibition of matrix protease activities. Previous studies have also identified TFPI‑2 in the nucleus, and a possible function of nuclear TFPI‑2 as a transcriptional repressor of matrix metalloproteinase‑2 (MMP‑2) was recently demonstrated. We are currently establishing TFPI‑2 as a serum biomarker for OCCC patients; however, TFPI‑2 expression in OCCC tissues has not been previously investigated. In the present study, we examined TFPI‑2 expression and its localization in 11 OCCC cell lines by western blotting and enzyme‑linked immune assay. Four cell lines expressed TFPI‑2 in the nucleus, cytoplasm and culture plate-attached extracellular fraction, while four other cell lines expressed TFPI‑2 only in the extracellular fraction. In the remaining three cell lines, TFPI‑2 was not identified in any fraction. The amount of secreted soluble TFPI‑2 showed similar trends to that of the plate‑attached fraction. We next investigated the expression levels and distribution of TFPI‑2 in surgically resected EOC tissues by immunohistochemistry. In 52 of the 77 (67.5%) OCCC tumors, TFPI‑2 expression was detected in at least one of the nuclear, cytoplasmic and extracellular matrix fractions. In contrast, we did not identify TFPI‑2 in the other EOC subtypes (n=65). TFPI‑2‑positive expression distinguished CCC from the other EOC tissues with a sensitivity of 67.5% and specificity of 100%. Although the inherent tumor suppressor function, statistical analyses failed to demonstrate correlations between TFPI‑2 expression and clinical parameters, including 5‑year overall survival, except for the patient age. In conclusion, we identified TFPI‑2 expression in the nucleus, cytoplasm and extracellular matrix in OCCC tissues. The high specificity of TFPI‑2 may support its use for diagnosis of OCCC in combination with existing markers.
Keywords: TFPI-2; ovarian clear cell carcinoma; immunohistochemistry; biomarker; subcellular localization.