Ki67 as a prognostic factor in low grade serous ovarian cancer (LGSOC): A retrospective analysis of the Tumor Bank Ovarian Cancer (TOC).

Abstract

5562 Background: LGSOC is a rare and distinct entity characterized by younger age, lower response to chemotherapy and better clinical outcome. Aim of this study was to evaluate the impact of Ki67, estrogen and progesterone receptors (ER and PR) on platinum response and survival in primary LGSOC patients. Methods: 80 primary LGSOC patients with available FFPEs were identified within TOC. The histology was confirmed at a second histological evaluation. For Ki67 analysis conventional immunohistochemical staining was performed with the Mib-1 clone on Ventana. Slides were explored with a light microscope camera. A representative field for Ki-67 evaluation was selected, in case of heterogeneous staining a hot spot was chosen. The software classified detected cells into non-tumor, negative and positive cells. When necessary, a correction of tumor and non-tumor areas was performed by an experienced pathologist. The counted cells ranged between 175 and 2398. Overall the method allows a precise, continuous and standardized means to quantify Ki-67. ER and PR status was determined on scanned IHC TMA slides. ER and PR positive tumors were defined if the percentage of stained tumor cells was at least 10%. Statistical analysis was performed using IBM SPSS Statistics. Results: Median age at diagnosis was 56 years (range: 20-81), 81.3% of patients presented in advanced stage and 96.3% received platinum based chemotherapy. Ki67 median value was 5.09 (IQR: 1.56-10.5). 93.1% and 47.9% of the patients showed ER and PR positive tumors, respectively. Median overall survival (OS) was 45.5 months (range: 0.1-182.8). Our analysis showed that platinum free interval (PFI) was significant longer in patients with lower Ki67 (p = 0.006). Higher proliferation rates were significant associated with poorer progression free (p = 0.011, HR = 1.039, 95%CI: 1.009-1.070) and OS rates (p = 0.001, HR = 1.059, 95%CI: 1.025-1.095). No differences in clinical outcome were seen in patients with different ER and PR status. Conclusions: This is the first study showing that higher Ki67 values correlate with shorter PFI and poorer survival rates in LGSOC, underlying the heterogeneous character of this disease.