Characterization of kallikrein-related peptidase 4 (KLK4) mRNA expression in tumor tissue of advanced high-grade serous ovarian cancer patients

Abstract

Overexpression of several members of the kallikrein-related peptidase (KLK) family, including KLK4, has been reported in ovarian cancer tissue, consistent with the fact that elevated levels of KLK protein are often also found in serum and in effusion fluids of ovarian cancer patients. In the present study, we quantitatively analyzed KLK4 tumor tissue mRNA expression levels in a homogeneous cohort including 138 patients of advanced high-grade serous ovarian cancer (FIGO stage III/IV). Age as well as ascites fluid volume were found to be significantly associated with KLK4 mRNA expression levels. In univariate Cox regression analysis, the clinical factors residual tumor mass and ascites fluid volume represented univariate predictors for both overall survival (OS) and progression-free survival (PFS). Furthermore, elevated KLK4 mRNA expression levels were significantly linked with reduced OS (p = 0.001), but not with PFS. The results concerning the association of KLK4 mRNA expression with OS were validated in a publicly available Affymetrix-based mRNA data set from The Cancer Genome Atlas (n = 252) applying the Kaplan-Meier Plotter tool (p = 0.047). In multivariable analyses, elevated KLK4 mRNA values turned out as an additional, independent predictive marker for shortened OS (p = 0.006), whereas residual tumor mass, but not ascites fluid volume, remained an independent indicator for both OS and PFS (p < 0.001 and p = 0.002, respectively). The results of the present study, obtained in a well-defined, homogenous cohort of patients afflicted with advanced high-grade serous ovarian cancer, are in line with previous reports describing high KLK4 levels as an unfavorable marker in ovarian cancer patients.

Fig 1. KLK4 mRNA expression levels in tumor tissues of patients afflicted with advanced high-grade serous ovarian cancer (FIGO III/IV).

The cumulative histogram depicts relative KLK4 mRNA expression levels (normalized to HPRT mRNA levels). Most samples display very low expression. For further analysis, we categorized the KLK4 mRNA expression levels into low expression versus high expression groups by the 50^th percentile (median).

Fig 2. Probability of PFS and OS of patients with advanced high-grade serous ovarian cancer (FIGO III/IV) as stratified by KLK4 mRNA expression levels in primary tumor tissues.

Patients with high KLK4 mRNA expression levels display a significantly worse OS rate (Kaplan-Meier analysis, p = 0.001) (A) but not PFS (B), compared to patients with low KLK4 mRNA expression levels.

Fig 3. Validation of significant associations between KLK4 mRNA expression and patient outcome in a publicly available Affymetrix microarray data set.

The microarray data set analyzed for KLK4 mRNA expression (probe ID 1555737_a_at) was from The Cancer Genome Atlas (TCGA). The patients were selected for serous histological type, advanced stage (FIGO III/IV), high-grade (grade 3), platinum-containing chemotherapy, and 5 years’ follow-up. This selection resulted in a patient cohort encompassing 252 patients for analysis of the association with OS (A) and 249 patients for PFS (B), respectively.