P53 mutations in tissue from Danish ovarian cancer patients

Abstract

Objectives.

The p53 gene, a tumor suppressor gene located on the short arm of chromosome 17 (17p13), has been found mutated in 30–80% of epithelial ovarian cancers (OC), with the most frequently detected mutations in the conserved regions of the gene. A small number of studies investigated the survival of patients with p53 mutations in OC, but their conclusions are not in agreement.

Methods.

We analyzed the frequency of p53 mutations in 124 Danish women with OC, using Single-Stranded Conformation Polymorphism analysis in addition with DNA sequencing and evaluated if mutations correlated with clinicopathological parameters and with patient survival.

Results.

Thirty-five (28%) ovarian tumors were found to contain one or more p53 variations, two of which were considered polymorphisms. Twenty-seven (82%) mutations were single nucleotide substitutions of which 23 (85%) were missense mutations and therefore led to amino acid substitutions. Significantly shorter survival was found for stage III/IV patients with a p53 missense mutation compared to stage III/IV OC patients with wild type p53 (P = 0.0018). Multivariate Cox regression analysis restricted to 107 OC patients with a p53 missense mutation or p53 wild type in the tumor tissue and with information on radicality of primary surgery showed that missense p53 mutation (HR = 2.5, 95% CI: 1.21–4.98), radicality after primary surgery (HR = 1.7, 95% CI: 1.04–2.88), tetranectin (mg/l: HR = 0.78, 95% CI: 0.67–0.91) and stage (I vs. III: HR = 0.30, 95% CI: 0.10–0.92, II vs. III: HR = 0.24, 95% CI: 0.05–1.05, IV vs. III: HR = 2.70, 95% CI: 1.22–5.98) were independent prognostic factors.

Conclusion.

Missense mutations in the conserved regions of p53 may be of prognostic value in Danish OC patients.

Introduction

Ovarian cancer (OC) is the leading cause of death among gynaecologic cancer patients and is the fifth most frequent female cancer type and the fourth most frequent cause of death from cancer among women in Denmark [1]. If diagnosed and treated at early stage of disease, approximately 90% of OC patients survive 5 years or longer. However, if diagnosed at an advanced stage of disease (FIGO stage III and IV) (The International Federation of Gynecology and Obstetrics staging), the survival rate diminishes to less than 20%. Unfortunately, 70% of cases are diagnosed at the late stage of disease [2], [3]. The high frequency and poor prognosis of OC emphasize the need for both additional and better prognostic factors.

The molecular genetic events underlying ovarian neoplasms are complex and poorly understood. The transformation of a normal cell into a malignant cell is thought to be a multistep process that progresses through an accumulation of genetic alterations in two categories of normal cellular genes: protooncogenes and tumor suppressor genes [4], [5], [6].

The p53 tumor suppressor gene, on chromosome 17p13.1, encodes a 393 amino acid nuclear phosphoprotein (the p53 protein), thought to have a major function as a negative regulator of the cell cycle [7]. The p53 tumor suppressor gene has been found mutated in 30–80% of epithelial OCs depending on the methods used [5], [8], [9], [10], [11], [12], [13], [14], [15], [16]. Generally, most of these missense mutations are found corresponding to the sequence-specific DNA-binding domain of the p53 protein, resulting in loss of function [17], [18], [19]. Only few studies investigated the prognostic role of p53 mutations in OC patients, and the results of the five most recently published studies are not consistent [11], [12], [13], [15], [20]. The prognostic role of p53 mutations is therefore still a subject of debate.

Serum levels of CA125, a biochemical marker for OC, are elevated in more than 80% of epithelial OCs. In studies using univariate life tables analysis, the level of CA125 has been reported to be a valuable prognostic marker of primary OC [21], [22]. However, the prognostic value of CA125 determination disappears when FIGO stages are included in multivariate Cox analyses [22], [23]. In contrast, tetranectin (TN) has been shown of prognostic value in OC patients when adjusted for FIGO stage [24], [25], [26]. Low serum or plasma TN levels may be due to absorption of TN from the blood to the tumor site for the purpose of proteolysis. This hypothesis is supported by the immunohistochemical findings of high extracellular TN concentrations in the malignant tumors in combination with low plasma TN values [27].

The aim of this study was to determine the frequency of p53 mutations in tissue from 124 Danish OC patients, to evaluate whether mutations correlated with clinicopathological parameters, to investigate the correlation of p53 mutations with CA125 and TN and finally to evaluate the role of p53 mutation as a prognostic factor in Danish OC patients.