TP53 mutations are common in all subtypes of epithelial ovarian cancer and occur concomitantly with KRAS mutations in the mucinous type

Highlights

• TP53 mutations are common in all subtypes of epithelial ovarian cancer.

• TP53 and KRAS mutations occur frequently concomitant in ovarian mucinous cancer.

• Deep-sequencing allows a reliable and fast detection of mutations in FFPE tissue.

• These mutations are applicable for molecular stratification of ovarian cancer.

Abstract

Aims

Epithelial ovarian cancer (EOC) can be classified into four major types (serous, endometrioid, clear cell, mucinous). The prevalence of driver gene mutations in the different subtypes is controversial. High-grade serous carcinomas show frequent TP53 mutations, whereas KRAS and BRAF mutations are less common. In non-serous EOC, the relevance of these gene mutations remains to be elucidated.

Methods

We investigated 142 formalin-fixed, paraffin-embedded EOC, including serous (n = 63), endometrioid (n = 29), clear cell (n = 25), mucinous (n = 14), and others (n = 11) for mutations in TP53 exons 5–8, KRAS exons 2 and 3, and BRAF exon 15 by pyro-sequencing using the GS Junior 454 platform. The mutational status was correlated with clinicopathological features and patient overall survival.

Results

We identified mutations in the coding region of TP53 in 51.4% (73/142), and of KRAS in 9.9% (14/142) but not of BRAF. TP53 mutations occurred frequently not only in high-grade serous carcinomas (58.7%), but also in mucinous (57%) and clear cell EOC (52%). TP53 mutations were associated with high-grade carcinomas (p = 0.014), advanced FIGO stage (p = 0.001), intraoperative residual disease > 1 cm (p = 0.004), as well as poor overall survival (p = 0.002). KRAS mutations were mainly identified in mucinous EOC (57%) and were concomitantly with TP53 mutations in five mucinous carcinomas (36%).

Conclusions

TP53 gene driver mutations are a common feature of all advanced ovarian cancer subtypes, whereas BRAF mutations seem to be a rare event in EOC. KRAS mutations with synchronous TP53 mutations occur predominantly in low-grade mucinous carcinomas, suggesting a specific molecular background of this ovarian cancer type.

Introduction

Ovarian cancer has the highest mortality rate among gynaecological malignancies in the Western world (Siegel et al., 2012). Due to the absence of early clinical symptoms, the majority of the patients are diagnosed with an advanced disease stage. Despite many efforts in ovarian cancer research, reliable prognostic and predictive biomarkers are still not available. In the last decade, molecular studies have shown that the histological subtypes of ovarian cancer are associated with different genetic alterations and biological behaviour as well as response to chemotherapy (Bast et al., 2009, Prat, 2012).

Recent molecular studies have mainly focused on the common serous histological subtype and little is known about the non-serous subtypes. The Cancer Genome Atlas Research Network (TCGA) and Ahmed et al. have demonstrated that high-grade serous cancer is characterized by TP53 mutations in up to 96% of the cases (Ahmed et al., 2010, Anon, 2011). Both studies identified exons 5–8 of TP53 as the most frequently mutated region with 89% and 81.5%, respectively (Ahmed et al., 2010, Anon, 2011). Previous studies have shown that TP53 mutations are highly prevalent in high-grade serous carcinomas when compared to low-grade serous carcinomas or serous borderline tumours (Salani et al., 2008, Singer et al., 2005). TP53 mutations were further reported in high-grade endometrioid and transitional cell carcinomas (Cuatrecasas et al., 2009, Kolasa et al., 2006). In contrast, KRAS and BRAF mutations were found in low-grade serous carcinomas and its precursors (Singer et al., 2003, Sieben et al., 2004). BRAF mutations seem to be restricted to low-grade serous neoplasms, whereas KRAS mutations were identified in mucinous carcinomas and its precursors as well as in endometrioid and clear cell subtypes (Auner et al., 2009, Mayr et al., 2006, Sieben et al., 2004). However, in these publications the TP53, KRAS, and BRAF mutation status was not assessed simultaneously.

Deep-sequencing technology allows the detection of mutations in multiple target regions in parallel within the tumour population of a patient. In a recent study, we assessed the TP53 mutation status in endometrial carcinomas by ultra-deep-sequencing with input DNA that derived from formalin-fixed and paraffin-embedded (FFPE) tissue (Wild et al., 2012). Furthermore, we demonstrated the reliability of this method for other targets such as BRAF using FFPE material (Rechsteiner et al., 2013) and using DNA derived from fresh frozen tissue (Gerstung et al., 2012).

Consequently, we aimed to characterize a broad spectrum of human epithelial ovarian carcinomas for specific cancer-causing mutations in TP53 (exons 5–8), KRAS (exons 2 and 3), and BRAF (exon 15) by a high-throughput deep-sequencing approach with DNA derived from FFPE. We further compared the mutational profile among different histological subtypes, clinicopathological factors, and with patient overall survival.