l-DOPA Decarboxylase (DDC) Expression Status as a Novel Molecular Tumor Marker for Diagnostic and Prognostic Purposes in Laryngeal Cancer.

l-DOPA decarboxylase (DDC) plays an essential role in the enzymatic synthesis of dopamine and alterations in its gene expression have been reported in several malignancies. Our objective was to analyze DDC messenger RNA (mRNA) and protein expression in laryngeal tissues and to evaluate the clinical implication of this molecule in laryngeal cancer. In this study, total RNA was isolated from 157 tissue samples surgically removed from 100 laryngeal cancer patients. A highly sensitive real-time polymerase chain reaction methodology based on SYBR Green I fluorescent dye was developed for the quantification of DDC mRNA levels. In addition, Western blot analysis was performed for the detection of DDC protein. DDC mRNA expression was revealed to be significantly downregulated in primary laryngeal cancer samples compared with their nonmalignant counterparts (P = .001). A significant negative association was also disclosed between DDC mRNA levels and TNM staging (P = .034). Univariate analysis showed that patients bearing DDC-positive tumors had a significantly decreased risk of death (hazard ratio = 0.23, P = .012) and local recurrence (hazard ratio = 0.32, P =.006), whereas DDC expression retained its favorable prognostic significance in the multivariate analysis. Kaplan-Meier curves further demonstrated that DDC-positive patients experienced longer overall and disease-free survival periods (P = .006 and P = .004, respectively). Moreover, DDC protein was detected in both neoplastic and noncancerous tissues. Therefore, our results suggest that DDC expression status could qualify as a promising biomarker for the future clinical management of laryngeal cancer patients.