The tissue factor pathway inhibitor-2 (TFPI2) was recently identified as a diagnostic serum marker for ovarian clear cell carcinoma. Moreover, the immunohistochemical expression of TFPI2 in ovarian clear cell carcinoma was recently reported. This single-center retrospective study aimed to evaluate whether TFPI2 can be a specific biomarker for immunohistological diagnosis of endometrial clear cell carcinoma (ECCC). Immunohistochemical staining of TFPI2 in 55 endometrial carcinomas was evaluated at Nara Medical University Hospital. Thirteen ECCC samples were included as cases and 42 samples were included as a control (endometrioid carcinoma grade 1, 11 cases; grade 2, 11 cases; grade 3, 10 cases; serous carcinoma, 10 cases). The mean ± SD TFPI2 histoscore for diagnosing ECCC was 115.4 ± 87.9, which was significantly higher than that of non-ECCC (21.3 ± 45.9, P = 0.002). The best TFPI2 histoscore value obtained from the analyses of receiver operating characteristic curves for immunohistochemical diagnosis of ECCC was 15. With TFPI2 histoscores ≥15.0 as positive and <15.0 as negative, all 13 ECCC cases (100%) were positive for TFPI2, whereas 11 (26.2%) non-ECCC cases were positive for TFPI2. The sensitivity and specificity of TFPI2 for diagnosing ECCC were 100% and 73.8%, respectively. TFPI2 is expressed in ECCC and is useful for histopathological diagnosis.
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