Immunohistological analysis of stress-induced phosphoprotein 1 in ovarian cancer patients with low serum cancer antigen 125 levels

Objective: Stress-induced phosphoprotein 1 (STIP1) was recently identified as a potential tumor marker for human ovarian cancer. This study further evaluates the usefulness of STIP1 in ovarian tumor patients with normal CA125 serum levels. Materials and Methods: STIP1 and CA125 were immunohistochemically analyzed in 84 primary ovarian cancer and 30 benign ovarian tumors in patients with serum CA125 levels<35U/mL before surgery. Histoscores (0-300) were calculated as staining intensities (0-3) multiplied by percentage of tumor tissue (0-100%). Results: The cell types of the 84 cancers included 11 serous, 10 clear-cell, 51 mucinous, and 12 endometrioid carcinomas. There were 55 patients with invasive cancer and 29 with borderline ovarian tumors. The histoscores of STIP1, but not of CA125, in invasive cancer(mean±SD, 186.3±82.5) were significantly (p < 0.0001) higher than those seen in borderline ovarian tumors (86.2±85.5). WhentheSTIP1 histoscore was set at 183.8, invasive cancers (n = 55) were identified from benign tumors (n = 30) with a sensitivity of56.4%,a specificity of 93.3%, a positive predictive value of 93.9%, and a negative predictive value of 53.8%. Results of receiver operatingcharacteristics analysis showed that the area under curve of the STIP1 histoscore was 0.755, which was superior to that of CA125 (0.599). Conclusion: STIP1 histoscores may be useful in detecting invasive human ovarian cancer in patients with low serum CA125 levels.