The current TNM staging and histopathological grading systems are useful prognostic indicators for SSCC. However, they have limitations with regard to providing critical information regarding patient prognosis. Patients with the same clinical stage and/or pathological grade of SSCC often display considerable variability in disease recurrence and survival[1, 28]. Therefore, new objective measures and biomarkers are necessary to effectively differentiating patients with favorable outcomes from those with less favorable outcomes. Molecular biomarkers in conjunction with standard TNM and histopathological strategies have the potential to predict prognoses more effectively.
DJ-1 protein is coded by exons 27, contains 189 amino acids, and weights about 20 kD, and was firstly defined as an oncogene candidate in 1997. Recent studies showed that DJ-1 is expressed highly in many types of human malignancies[2, 5–15]. Lines of evidence have also suggested that the over-expression of DJ-1 is correlated with more aggressive clinical behaviors of pancreatic, esophageal and lung cancers[10–13]. However, in our recent glottic squamous cell carcinoma study, DJ-1 has only been identified as a prognostic marker and activator of cell proliferation, and the expression of DJ-1 was not correlated to clinical lymph node metastasis. This non-invasive role of DJ-1 in glottic squamous cell carcinoma which is contradictory to the invasive role of DJ-1 in other malignancies may be attributed to the clinical and biological behavior of glottic squamous cell carcinoma, as this type of LSCC was poorly invaded in clinic. So, in order to identify whether DJ-1 also play the invasive role in LSCC, SSCC, the more aggressive type of LSCC, was selected in the present study.
Recently, several studies showed that PTEN in human malignancies is associated with cell proliferation, tumor invasion, and TNM stage, and can be down-regulated by DJ-1 in several cancers, such as renal cancer, breast cancer, bladder cancer, and ovarian cancer[8, 24–26]. In 2005, Kim RH found that DJ-1 could activate cell proliferation and transformation by negatively regulating PTEN expression in breast cancer cells. In 2012, Lee H showed that over-expression of DJ-1 and loss of PTEN are associated with invasive urothelial carcinoma of urinary bladder. Taken together, we hypothesized that DJ-1 would promote migration and invasion of SSCC via down-regulating the expression of PTEN, and may associated with clinical lymph node status in SSCC.
In the immunohistochemistry-based study, we examined the expression of both DJ-1 and PTEN in SSCC tissue versus adjacent non-cancerous tissue. Our results indicate that the expression of DJ-1 was mainly in SSCCs and less frequently in adjacent non-cancerous tissues, whereas PTEN staining of adjacent non-cancerous tissues was stronger and more common than that of SSCCs (Figure1A, B). Furthermore, an significant difference in grade of DJ-1 expression was demonstrated between SSCCs and adjacent non-cancerous tissues (P < 0.001), and pT status (P = 0.003) and nodal status (P = 0.009) were linked to DJ-1 expression. This scenario is similar to that observed in other type of human cancers[5–13], and the relationship between nodal status and DJ-1 expression in SSCC revealed that DJ-1 may play an invasive role in SSCC. In both univariate and multivariate survival analysis, our study suggests that DJ-1, a prognostic marker for GSCC in our previous study, is also a prognostic marker in SSCC (Figure1C). Thus, expression of DJ-1 appears to have the potential to predict SSCC patients’ outcome.