Urokinase plasminogen activator receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1) are potential predictive biomarkers in early stage oral squamous cell carcinomas (OSCC)

Abstract

Oral squamous cell carcinoma (OSCC) is often associated with metastatic disease and a poor 5 year survival rate. Patients diagnosed with small tumours generally have a more favourable outcome, but some of these small tumours are aggressive and lead to early death. To avoid harmful overtreatment of patients with favourable prognosis, there is a need for predictive biomarkers that can be used for treatment stratification. In this study we assessed the possibility to use components of the plasminogen activator (PA) system as prognostic markers for OSCC outcome and compared this to the commonly used biomarker Ki-67. A tissue-micro-array (TMA) based immunohistochemical analysis of primary tumour tissue obtained from a North Norwegian cohort of 115 patients diagnosed with OSCC was conducted. The expression of the biomarkers was compared with clinicopathological variables and disease specific death. The statistical analyses revealed that low expression of uPAR (p = 0.031) and PAI-1 (p = 0.021) in the tumour cells was significantly associated with low disease specific death in patients with small tumours and no lymph node metastasis (T1N0). The commonly used biomarker, Ki-67, was not associated with disease specific death in any of the groups of patients analysed. The conclusion is that uPAR and PAI-1 are potential predictive biomarkers in early stage tumours and that this warrants further studies on a larger cohort of patients.

Figure 1. Staining pattern for uPAR, PAI-1 and uPA in OSCC.

Representative photomicrographs of tissue microarray sections stained for the markers A) uPAR, B) PAI-1 and C) uPA. Positive staining is seen as brown colour, nuclei are stained blue with haematoxylin. Scalebar = 50 µm. T = Tumour. S = Stroma.

Figure 2. Cytoplasmic and membrane staining of uPAR.

Representative photomicrographs of tissue microarray sections stained for uPAR, showing typical A) membrane and B) cytoplasmic localized staining of the tumour cells. Scalebar = 50 µm. Positive uPAR staining is seen as brown colour, nuclei are stained blue with haematoxylin.

Figure 3. Staining intensity of uPAR and PAI-1 in OSCC.

Representative photomicrographs of tissue microarray cores showing strong and weak staining for uPAR and PAI-1 in tumour islands: A) strong uPAR staining, B) weak uPAR staining, C) strong PAI-1 staining, and D) weak PAI-1 staining. Positive uPAR and PAI-1 staining is seen as brown colour, nuclei are stained blue with haematoxylin. Scalebar = 100 µm. T = Tumour. S = Stroma.

Figure 4. Staining of uPAR and PAI-1 in normal buccal mucosa tissue.

Representative photomicrographs of normal buccal mucosa tissue showing weak staining for uPAR (A) and PAI-1 (B) in the epithelial layer. Positive staining is seen as brown colour, nuclei are stained blue with haematoxylin.

Figure 5. Disease specific survival of patients with T1N0 tumours.

Kaplan-Meier survival plot showing probability for a disease specific survival based on A) uPAR, B) PAI-1, C) uPA and D) Ki-67 expression and related to months after diagnosis. Total number of patients included in the analysis was 27 for uPAR and Ki-67, and 26 for PAI-1 and uPA. *; p<0.05 was regarded as statistically significant.

Figure 6. Correlation between uPAR and PAI-1 expression in T1N0 tumours.

The correlation between the final scores of uPAR and PAI-1 in T1N0 tumours (N = 26) are presented in a Scatter plot (Spearman's Rho correlation coefficient = 0.566, p = 0.003). The regression line and the 95% confidence interval lines are indicated.