Differential cyclooxygenase expression levels and survival associations in type I and type II ovarian tumors

Abstract

Background: High cyclooxygenase (COX)-2 expression in ovarian tumors has been associated with poor prognosis, but the role of COX-1 expression and its relation to survival is less clear. Here, we evaluated COX expression and associations with survival outcomes between type I (clear cell, mucinous, low grade endometrioid and low grade serous) and type II (high grade serous and high grade endometrioid) ovarian tumors.

Methods: We developed and validated a new COX-1 antibody, and conducted immunohistochemical (IHC) staining for COX-1 and COX-2 on a tissue microarray (TMA) of 190 primary ovarian tumors. In addition to standard IHC scoring and H-scores to combine the percentage of positive cells and staining intensity, we also measured COX-1 and COX-2 mRNA expression by QPCR. High expression was defined as greater than or equal to median values. Clinical characteristics and disease outcomes were ascertained from medical records. Associations with disease-free survival (DFS) and overall survival (OS) were quantified by hazard ratios (HRs) and confidence intervals (CIs) from proportional hazards regression.

Results: Type I tumors had high COX-2 expression, while type II tumors had high COX-1 expression. In multivariable adjusted regression models, higher COX-1 mRNA expression was associated with shorter DFS (HR: 6.37, 95% CI: 1.84-22.01) and OS (HR: 2.26, 95% CI: 1.04-4.91), while higher H-scores for COX-2 expression were associated with shorter DFS (HR: 1.92, 95% CI: 1.06-3.49). Stratified analysis indicated that COX-2 was significantly associated with DFS among cases with Type II tumors (HR: 1.93, 95% CI: 1.06-3.53).

Conclusions: These findings suggest that ovarian tumor type contributes to differences in COX expression levels and associations with survival.

Keywords: Cyclooxygenase; Ovarian cancer; Survival analysis; Tumor subtype.

Fig. 1

Representative IHC Images for COX-1 and COX-2, the Vanderbilt TROC. Representative immunohistochemical staining for COX-1 and COX-2 in a high-grade serous (VOC-A-155) section from a TMA of 190 ovarian tumors. Higher power images of the boxed areas are shown in the corresponding right panels. Scale bars represent 100 μM

Fig. 2

COX-1 and COX-2 protein expression in ovarian cancer. The percentage of tumor cells positive for COX-1 and COX-2 was determined by automated image analysis and then scaled by intensity for H-scores, ranging from 0 to 300. a Pearson correlation between expression levels of COX-1 and COX-2. H-scores for COX-1 and COX-2 expression in (b) serous, endometrioid, mucinous and clear cell tumors, and in (c) serous tumors versus all other epithelial tumors and type II tumors (high grade serous and high grade endometrioid) versus type I tumors (all other types). P-values from Student’s t-tests

Fig. 3

Kaplan-Meier Survival Functions for COX-1 and COX-2 by RNA-seq from TCGA. Normalized RNA-seq data downloaded from the Broad Firehose for 489 high grade serous (type II) cases, analyzed for (a) COX-1 and DFS, (b) COX-1 and OS, (c) COX-2 and DFS, and (d) COX-2 and OS. Solid line = lower than median COX expression; dotted line = median or higher COX expression. X-axis is overall survival time in months, Y-axis is percentage of cases remaining alive, P-values from Log-Rank tests