Association of Ki67 expression levels and therapy outcome in low-grade serous ovarian cancer.

Abstract

5577 Background: Low-grade serous ovarian cancers (LGSOC) characterize different clinical pattern and lower chemotherapy responsiveness. The expression level of Ki67 is associated with prognosis differences in this patient group. However, Ki67 has not been evaluated as prognostic marker and a predictor of therapy outcome until now. Methods: Patients with LGSOC and Ki67 expression results were identified in institutional database. Receiver-operator characteristics (ROC) curve analysis was performed to find cut off values of Ki67% to discriminate patients with residual tumor mass after surgery from maximal debulked patients, and platinum sensitive patients from platinum resistant patients. Odd ratios (OR) and 95% confidence intervals (95% CI) were calculated using univariate and multivariate logistic regression analysis. Two-sided tests p < 0.05 and are considered statistically significant at a 95% confidence interval. The statistical analysis was performed with the IBM SPSS Statistics 25.0. Results: A total of 68 patients with LGSOC were included. All patients underwent surgery and 15 (22.1%) patients had residual mass ( > 0 mm) after cytoreduction. Sixty-one (89.7%) patients received platinum based first-line chemotherapy. Forty-three patients revealed a recurrence ≥6 months and eleven < 6 months. Patients with Ki67 < 3.6% had significantly higher therapy-free interval (TFI≥6 months), (OR = 13.9, 95%CI 1.62-118.40, p = 0.016). In the multivariate analysis of TFI over 6 months including CA 125, age at diagnosis, peritoneal carcinomatosis and ascites ( > 500ml) Ki67 < 3.6% remained significant (OR = 17.6, 95%CI 1.56-197.52, p = 0.020). Moreover, Ki67% > 3.6% were associated with higher risk of residual mass after surgery (OR = 6.75, 95%CI 1.39-32.87, p = 0.018). Conclusions: It is the first study showing association between Ki67% expression and duration of TFI to platinum-based chemotherapy as well as outcome of the surgery in LGSOC. Further prospective trials should be planned to develop predictive models in this patients.