K-ras mutational status predicts poor prognosis in unresectable pancreatic cancer

Abstract

Objective

To determine the prognostic value of K-ras mutations in plasma DNA of unresectable pancreatic cancer patients.

Methods

Blood samples were collected from 91 patients with unresectable pancreatic cancer prior to treatment. K-ras gene was amplified from the circulating plasma DNA. Mutations were detected by direct sequencing. The relationship between the types of K-ras gene and prognosis of unresectable pancreatic cancer was evaluated.

Results

K-Ras codon 12 mutations were found in 30 of 91(33%) plasma DNA samples, 17mutations were c.35G > A (p.G12D), 11 were c.35G > T (p.G12V) and only 2 were c.34G > C (p.G12R)). K-ras codon 12 mutations could significantly reflect the clinical parameters, including TNM tumor staging (P = 0.033) and liver metastasis (P = 0.014). The median survival time of patients with K-ras mutations was shorter than that of patients with wild-type K-ras gene (3.9 months vs. 10.2 months, P < 0.001). K-ras codon 12 mutation from plasma DNA was an independent negative prognostic factor for survival (hazard ratio, 7.39; 95% confidence interval, 3.69–14.89).

Conclusion

K-ras mutation in plasma DNA is a predictive biomarker for a poor prognosis of unresectable pancreatic cancer patients.

Introduction

Pancreatic cancer is the fourth leading cause of cancer death in North America.¹ The prognosis is poor, and the 5-year survival rate is only 3–5%. The curative treatment for the pancreatic cancer is surgery, but the resectability rate is 15%–20% at the time of diagnosis.² Despite the recent advances in diagnostic techniques, it remains difficult to diagnose this devastating disease in the early stage. Most patients manifest a disseminated disease at initial diagnosis. The median survival time of patients with unresectable pancreatic cancer is less than 6 months.³

Numerous studies have been identified that the risk factors for pancreatic cancer are including advancing age, tobacco smoking, diet, diabetes mellitus and chronic pancreatitis.1, 4, 5 The prognostic factors for advanced pancreatic cancer described in literature include the baseline Karnofsky Performance status (KPS), high level of γ-glutamyl transpeptadase (GGT), serum carbohydrate antigen 19-9 (CA19-9)and TNM staging.6, 7, 8 Recently there are no molecular markers of clinical utility, or rationally designed, molecularly targeted therapies, for patients with pancreatic cancer.⁹ Therefore, it is necessary to find effective molecular markers which could classify patients into different risk categories and thus allow multi-modality treatment regimens to be better targeted toward individual’s condition.

In the past decades, extensive studies have indicated that the molecular alterations are associated with the pathology and prognostic value in patients with pancreatic cancer, such as K-ras, P16, LMO-4, LMO-2 and Smad7.9, 10, 11, 12 Previous studies have shown that between 70 and 90% of the pancreatic tumors harbor K-ras mutations (almost always confined to codon 12).¹³ K-ras mutations can be easily detected in clinical specimens (e.g., tissue samples, pancreatic juice and plasma) by methods such as PCR-Restriction Fragment Length Polymorphism, Mismatch ligation assay, modified Guanidine/Promega Resin, selective hybridization, Single Strand Conformation Polymorphism and Sequencing.2, 14, 15, 16 Mora et al. concluded that no variant sequences were detected between plasma and tumor tissue from pancreatic cancer patients.¹⁶ Previous studies have suggested that a significantly higher level of plasma DNA exists in the peripheral blood of patients with pancreatic cancer, identifying the genetic alterations in those patients could be helpful to assess the extent of the disease at the time of initial diagnosis.2, 17 Therefore, detecting K-ras mutations in pancreatic cancer through the circulating plasma DNA is a noninvasive and convenient method, it might be a useful molecular marker in clinical utility.

However, most studies in the past have focused on the resectable pancreatic cancer, 2, 14, 15 the prognostic value of K-ras mutations from plasma DNA remains unclear in unresectable pancreatic cancer patients.

The aim of this study was (1) to detect the mutational status of K-ras oncogene from plasma DNA in patients with unresectable pancreatic cancer; (2) to study the correlation between the medical features and K-ras mutations; and (3) to analyze the prognostic value of K-ras mutations from plasma DNA in patients with unresectable pancreatic cancer.