Clinical relevance of protein-tyrosine (de-)phosphorylation in head and neck cancer.

Previous studies have shown that protein tyrosine (de)phosphorylation plays an important role in head and neck cancer. Protein-tyrosine kinases (PTK) and protein-tyrosine phosphatases (PTPase) activities in the cytosol of tumor tissue were significantly increased compared to normal tissue of cancer patients as well as controls. Additionally, the enzyme activities in normal tissue of tumor patients were significantly higher than enzyme activities in normal tissue of the control group. In this paper, we have correlated the cytosolic and membranous PTK and PTPase activity of tumor and nontumor tissue with several clinical and histological parameters known to influence the clinical outcome. Furthermore, we have analyzed the value of the enzyme activities as an independent predictor of clinical behavior and occurrence of second primary tumors. We confirmed our earlier observations that cytosolic and membranous PTK activities and cytosolic PTPase activities in tumor tissues are increased compared to activities in nontumor tissues and controls. Moreover, we also confirmed the findings of increased enzyme activities in nontumor tissues compared to findings in control tissues. This finding in histologically proven healthy mucosa is highly interesting because it indicates that these biochemical changes are obviously not (yet) translated into morphological changes. Significant differences were found in membranous PTK activity when the patients were grouped by sex, tumor localization, lymph node metastasis, and previous radiotherapy. During the follow-up period, no relation could be found between enzyme activities in tumor and/or nontumor tissues and disease-free interval or occurrence of second primary tumors.