The prion-like protein doppel as a seurm biomarker for epithelial ovarian cancer

Abstract

Ovarian cancer has a dire prognosis with an overall 5-year survival rate of ~40%, whereas stage III and IV has a survival rate of only 3-19%. Failure to detect early contributes highly to the poor survival rate of ovarian cancer. Thus, early detection of EOCs is likely to translate into mortality benefit. Two tests used clinically to detect ovarian cancer are serum cancer antigen-125 (CA-125) and transvaginal ultrasound. Both have limitations of specificity and sensitivity. CA-125 along with other biomarkers that are in clinical trials express both in the ovaries and serum of healthy females. Thus, the specific detection among cancer-free controls versus ovarian cancer cases remains highly variable. We hypothesize to assess the Doppel (PRND gene) as a serum biomarker in the detection of epithelial ovarian cancers (EOC) at the early stages. Doppel, a prion-like protein first identified in 1996, is known to express in testis and appears to regulate male fertility. Previously, we and others reported that Doppel is a highly specific tumor endothelium marker. In this study, to validate the potential of Doppel as an EOC serum biomarker, using ELISA, we detected Doppel concentration in the sera of 76 sera samples from patients with stage and histopathology information, and in 18 normal human sera (NHS). Doppel level was significantly higher in sera of EOC patients than NHS (0.720 vs 6.653 ng/ml, p<0.0001); 72 out of 76 patients were positive for Doppel expression (cut off value was calculated as Mean+3×SEM = 1.296 ng/mL) while only 3 out of 18 cases were positive for NHS. Receiver operating characteristic (ROC) analysis showed that Doppel can differentiate EOC patients from normal individuals with AUC of 0.957, sensitivity of 90.8%, and specificity of 90%. Doppel was markedly higher in all stages of EOC than NHS (Stage I, 6.261 ng/mL; Stage II, 8.045 ng/ml; Stage III, 7.040 ng/mL; and Stage IV, 5.726 ng/ml vs NHS 0.720 ng/ml; p<0.001). Interestingly, serum Doppel level was higher among EOC of serous adenocarcinoma (7.020 ng/mL; n = 39), mucinous (10.780 ng/mL; n = 8), and endometroid (7.295 ng/mL; n = 7) than clear cell (3.114 ng/mL; n = 7) or other types (4.855 ng/mL; n = 15). Together, our study showed the potential of Doppel as a serological biomarker for EOC detection.