Expression of cyclooxygenase 2 is an independent prognostic factor in human ovarian carcinoma

Abstract

Cyclooxygenase-2 (COX-2) is the rate-limiting enzyme in prostanoid biosynthesis and is involved in tumor progression. We investigated expression of COX-1 and COX-2 in cell lines and tumors from ovarian carcinomas. Expression of COX-2 mRNA and protein was detectable in three of five ovarian carcinoma cell lines and was inducible by interleukin-1beta or phorbolester in a subset of cell lines. Prostaglandin E(2) (PGE(2)) production could be inhibited by the selective COX-2 inhibitor NS-398. In malignant ascites of ovarian carcinomas significantly increased levels of PGE(2) were found compared to other carcinomas or nonmalignant ascites (P = 0.03). We investigated expression of COX-2 by immunohistochemistry in 117 ovarian surface epithelial tumors. Expression of COX-2 was detected in 42% of 86 ovarian carcinomas and in 37% of 19 low malignant potential tumors, but not in 12 cystadenomas or 2 normal ovaries. Expression of COX-1 was detected by immunohistochemistry in 75% of 75 invasive ovarian carcinomas and in 75% of 16 low malignant potential tumors, whereas 2 samples from normal ovaries and 8 cystadenomas were positive for COX-1. In univariate survival analysis of invasive carcinomas, expression of COX-2 was associated with a significantly reduced median survival time (log rank test, P = 0.04). For patients younger than 60 years of age, this association was even more significant (P < 0.004). In contrast, expression of COX-1 was no prognostic parameter (P = 0.89). There was no significant correlation between COX-2 or COX-1 expression and other clinicopathological markers. In multivariate analysis expression of COX-2 was an independent prognostic factor for poor survival (relative risk, 2.74; 95% CI, 1.38 to 5.47). Our data indicate that COX-2 expression is an independent prognostic factor in ovarian carcinoma. Based on the results of this study, it would be interesting to investigate whether ovarian carcinoma patients with tumors positive for COX-2 would benefit from treatment with selective COX-2 inhibitors.

Figure 1.

Expression of COX-1 and COX-2 mRNA in ovarian carcinoma cell lines. Human ovarian carcinoma cell lines were stimulated with IL-1β or TPA for 6 hours. Expression of COX-1, COX-2, and GAPDH mRNA was investigated by RT-PCR. One of three independent experiments is shown.

Figure 2.

Expression of COX-1 and COX-2 protein in ovarian carcinoma cell lines. Human ovarian carcinoma cell lines were stimulated with IL-1β or TPA for 24 hours. Expression of COX-1, COX-2, and β-actin was investigated by immunoblotting. One of three independent experiments is shown.

Figure 3.

Production of PGE₂ in ovarian carcinoma cell lines. A: OVCAR-3 cells were stimulated with IL-1β for 24 hours with or without the addition of NS-398 (50 μmol/L). B: CAOV-3 cells were stimulated with TPA for 24 hours with or without NS-398. PGE₂ in supernatant was measured by specific ELISA. Mean and SD from three independent experiments is shown.

Figure 4.

Expression of COX-1 and COX-2 mRNA in 10 cases of ovarian tumors. RNA from samples of ovarian carcinoma tissue was isolated and expression of COX-1, COX-2, and GAPDH mRNA was investigated by RT-PCR. Histological diagnoses: 1, serous papillary ovarian carcinoma, G3; 2, clear cell ovarian carcinoma, G2; 3, malignant mixed Mullerian tumor; 4, serous papillary ovarian carcinoma, G1; 5, serous papillary ovarian carcinoma, G3; 6, endometrioid ovarian carcinoma, G3; 7, endometrioid ovarian carcinoma, G2; 8, serous papillary ovarian carcinoma, G3; 9, serous LMP tumor; 10, serous papillary ovarian carcinoma, G3.

Figure 5.

Production of PGE₂ in ascitic fluid. PGE₂ in ascitic fluid was measured by specific ELISA in five cases of ovarian carcinoma,, five non-ovarian malignancies, and six cases of nonmalignant ascites (liver cirrhosis). Mean and SEM is shown; *, P = 0.03, Student’s t-test.

Figure 6.

Expression of COX-1 and COX-2 in normal ovaries, LMP tumors, as well as ovarian carcinomas investigated by immunohistochemistry. Normal ovarian surface epithelium was positive for COX-1 (A), but negative for COX-2 (B). A mucinous ovarian carcinoma negative for COX-1 (C), but positive for COX-2 (D). Positive cytoplasmatic staining of COX-2 in an undifferentiated invasive ovarian carcinoma (E). LMP tumor negative for COX-2 (F).

Figure 7.

Univariate survival analysis (Kaplan-Meier) of all 86 patients with invasive ovarian carcinomas. A: Patients with tumors negative for COX-2 have an increased median survival time (52.47 months, n = 50) compared to patients with tumors positive for COX-2 (30.40 months, n = 36) (log rank test; P = 0.04). B: Patients <60 years of age have a longer median survival time (52.77) compared to patients >60 years of age (30.10 months, P < 0.02). C: For patients younger than 60 years of age with tumors negative for COX-2 the median survival time is not reached during the follow-up period of 110 months, whereas patients in the same age group with tumors positive for COX-2 have a median survival time of 34.63 months (P < 0.004). D: In contrast, for patients older than 60 years of age there are no differences in median survival time between patients with tumors negative for COX-2 (30.10 months) and tumors positive for COX-2 (36.13 months, P = 0.97).