Clinical relevance of the deregulated kallikrein-related peptidase 8 mRNA expression in breast cancer: a novel independent indicator of disease-free survival

Examining for new BC biomarkers has proven that kallikrein-related peptidase (KLK) family members represent promising serum and/or tissue molecular tools for early diagnosis, effective prognosis, and treatment monitoring of patients. The aim of this study was to investigate, the previously unexplored, prognostic significance of KLK8 in BC. KLK8 mRNA expression was quantitatively analyzed in 150 cancerous and 100 corresponding normal breast tissue specimens via a SYBR Green-based Real-Time PCR methodology. Expression data and patients' clinicopathological parameters were used for extensive biostatistical analyses, including internal validation. KLK8 mRNA expression was significantly downregulated in the cancerous tissue part relative to the non-cancerous counterpart (P < 0.001), in the majority of the paired breast tissue samples. KLK8 expression was associated with advanced TNM stage (P = 0.019) and positive nodal status involvement (P = 0.044). Triple negative (TNBC) and HER2 overexpressing tumors exhibited higher KLK8 expression levels (P < 0.001), compared to Luminal A and B molecular subtypes. Kaplan-Meier survival curve analysis revealed that BC patients with high KLK8 expression had significantly shorter disease-free survival (DFS) intervals (P < 0.001) compared to those belonging in the KLK8-low expression group. Cox univariate analysis confirmed the association between KLK8 expression, analyzed as a continuous variable, and poor patients' outcome (Hazard ratio [HR] = 3.28, P < 0.001). Most importantly, multivariate analysis showed that KLK8 expression is a strong and independent predictor of adverse DFS in BC ([HR] = 2.74; P = 0.002). Our results show that KLK8 mRNA expression is associated with aggressive tumor characteristics and it can serve as a novel independent biomarker of unfavorable prognosis for BC patients.