Cathepsin K associates with lymph node metastasis and poor prognosis in oral squamous cell carcinoma

Abstract

Background: Lymph node metastasis (LNM) is a major determinant of prognosis and treatment planning of oral squamous cell carcinoma (OSCC). Cysteine cathepsins constitute a family of proteolytic enzymes with known role in the degradation of the extracellular matrix. Involvement in pathological processes, such as inflammation and cancer progression, has been proved. The aim of the study was to discover the clinicopathological and prognostic implications of cathepsin K (CTSK) expression in oral squamous cell carcinoma.

Methods: Eighty-three patients with primary OSCC, treated surgically between 1996 and 2000, were included. Gene expression data were acquired from a previously reported study. Human papilloma virus (HPV) status was previously determined by an algorithm for HPV-16. CTSK Protein expression was semi-quantitatively determined by immunohistochemistry in tumor and stromal cells. Expression data were correlated with various clinicopathological variables.

Results: Elevated gene and protein expression of CTSK were strongly associated to LNM and perineural invasion (p < 0.01). Logistic regression analysis highlighted increased CTSK protein expression in tumor cells as the most significant independent factor of lymphatic metastasis (OR = 7.65, CI:2.31-23.31, p = 0.001). Survival analysis demonstrated CTSK protein expression in both stromal and tumor cells as significant indicators of poor 5-year disease specific survival (HR = 2.40, CI:1.05-5.50, p = 0.038 for stromal cells; HR = 2.79, CI:1.02-7.64, p = 0.045 for tumor cells).

Conclusion: Upregulation of CTSK seems to be associated with high incidence of lymphatic spread and poor survival in OSCC. CTSK could therefore serve as a predictive biomarker for OSCC.

Keywords: Cathepsin K; Lymph node metastasis; Oral squamous cell carcinoma; Prognosis.

Fig. 1

Schematic representation of the work flow of this study. Previous studies resulted in the discovery and validation of a multi-gene signature. In this study, gene expression data were used to correlate the selected gene CTSK with clinical and histopathological parameters. From the same cohort of tumor samples, a TMA was constructed for immunohistochemical analysis of the selected gene to correlate their protein expression with clinical and histopathological parameters, and outcomes were compared

Fig. 2

CTSK expression in OSCC and normal mucosa. Representative stainings of the TMA, consisting of 83 OSCC cases, are presented. CTSK is diffusely expressed, is stained both in tumor as in stromal cells and varies in expression from non to strong expression. Staining scores were calculated by the product of intensity (normal = 1, strong = 2) and the proportion of stained tumor or stromal cells (%). Panels a-f represent examples of CTSK staining; a) normal mucosa, b) OSCC negative for CTSK in stromal cells, c) OSCC with normal staining in tumor cells and in stromal cells, d) OSCC negative for CTSK, e) OSCC with a normal intensity (score = 1 × 50% = 50), f) OSCC with a strong intensity (score = 2 × 75% = 150)

Fig. 3

Kaplan Meier disease specific survival (DSS) plots for all patients with OSCC (n = 83). Cases were stratified according to differential expression of CTSK, and were dichotomized into low and high expression according to the determined cut-off point in panel a for gene expression (− 0.26) and in panel b and c for protein expression (25). P-values in a-c represent the Log-rank test of this group comparison and therefore differ from the significance levels of the Cox-regression analysis in Table 4. In all three analyses, high CTSK expression was strongly associated with a worse 5-year DSS