[Application of peripheral blood endonuclease activity assay in the auxiliary diagnosis and monitoring of ovarian cancer].

Objective: To investigate the potential of peripheral blood mononuclear cell (PBMC) endonuclease activity as a biomarker for the auxiliary diagnosis and monitoring of ovarian cancer. Methods: This cross-sectional study recruited a total of 182 participants from Fudan University Shanghai Cancer Hospital from March 2022 to July 2025. The cohort included 97 patients with malignant group [age: 53(45, 66)], 49 patients with benign group [age: 46(34, 51)], and 36 healthy controls [age: 47(41, 54)]. The endonuclease activity of PBMCs was quantified using a plasmid cleavage assay combined with agarose gel electrophoresis. The activity was calculated as the ratio of cleaved substrate to the total substrate, expressed as the R-value. Serum levels of carbohydrate antigen 125 (CA125) and human epididymis protein 4 (HE4) were also measured for all participants. The Mann-Whitney U test was employed to compare R values among the groups. Receiver operating characteristic (ROC) curve analysis was conducted to evaluate the diagnostic efficacy of the R-value alone and in combination with serum CA125 and HE4 for ovarian cancer. The area under the curve (AUC), optimal cut-off value, sensitivity, and specificity were determined. A total of 61 patients in the malignant group completed the first follow-up. From this cohort, 31 patients with malignant ovarian tumors were randomly selected for dynamic follow-up of R-value changes before and after chemotherapy, and the rank sum test was used to analyze the effect of chemotherapy on R-values. Results: The median R-value was significantly higher in the malignant group [0.565 (0.424, 0.735)] compared to the benign group [0.384 (0.270, 0.567)](Z=6.963,P<0.001) and the healthy control group [0.130 (0.095, 0.330)] (Z=4.117,P<0.001). ROC analysis revealed that at the optimal cut-off value of 0.23 (maximizing the Youden's index), the R-value alone for discriminating ovarian cancer (malignant vs. benign+healthy) yielded an AUC of 0.842 (95%CI 0.763-0.921), with a sensitivity of 93.84% and a specificity of 69.44%. The combination of the R-value with CA125 and HE4 improved the diagnostic performance for malignant ovarian tumors, achieving an AUC of 0.948 (95%CI 0.902-0.994), with a sensitivity of 95.95% and a specificity of 82.61%. For diagnosing early-stage ovarian cancer, the combination yielded an AUC of 0.852 (95%CI 0.774-0.930), with 100% sensitivity and 71.88% specificity. Furthermore, the post-chemotherapy R value (0.285±0.233) was significantly lower than the pre-chemotherapy value (0.561±0.121) (t=12.74, P<0.001). Conclusion: PBMC endonuclease activity has potential significance for the auxiliary diagnosis and therapeutic monitoring of ovarian cancer. The combination of PBMC endonuclease activity, CA125, and HE4 may facilitate the early detection of malignant ovarian tumors.