Upregulation of kallikrein‑related peptidase 5 is associated with the malignant behavior of colorectal cancer.

Kallikrein-related peptidase 5 (KLK5) is a serine protease that has exhibited upregulated expression in numerous types of human cancer. The present study assessed KLK5 expression in colorectal cancer (CRC) tissues, in order to determine its association with clinicopathological data and prognosis. The mRNA and protein expression levels of KLK5 were detected using reverse transcription‑quantitative polymerase chain reaction, immunohistochemistry and enzyme‑linked immunosorbent assay, respectively. KLK5 expression was detected in 48 paraffin‑embedded tumor tissue samples and corresponding tumor‑free areas within the same specimens, 40 paired normal and CRC frozen tissues, and serum samples from 70 patients with CRC (including 38 serum samples taken pre‑ and post‑surgery) and 53 healthy individuals. The results demonstrated that KLK5 protein was strongly expressed in CRC; however, its expression was hardly detected in the matched normal mucosal tissue. The KLK5 mRNA expression levels were significantly upregulated in CRC tissues compared with the paired normal tissues, and were higher in Dukes' stage C/D cancer than in stage A/B (P<0.001). Furthermore, sera from patients with CRC exhibited increased KLK5 levels, as compared with that of healthy volunteers (878.02 vs. 391.07 pg/ml; P<0.001). Serum KLK5 levels were also significantly higher in patients prior to surgery compared with post‑surgery (909.48±536.72 vs. 644.00±522.87 pg/ml; P<0.001). In addition, increased serum KLK5 levels were associated with CRC lymph node or distant metastasis (P=0.003), tumor‑lymph node‑metastasis stage (P=0.004), and Dukes' stage (P=0.005). The results of the present study indicated that the mRNA and protein expression levels of KLK5 were significantly upregulated in CRC tissues and sera, and were associated with an advanced tumor stage. Further studies may identify KLK5 as a biomarker of CRC recurrence or treatment response.