Methods: Paraffin-embedded material of 21 primary ACCs and 15 normal salivary glands were investigated using immunohistochemistry. ACCs were located in the major (n=19) and minor (n=2) salivary glands. Male-female ratio was 1:1.3, mean age at diagnosis 51.7 years (25-81) and mean follow up time 72.8 months(7-128). 48% of patients developed recurrence/metastasis. 29% of patients died of disease. Expression of cell cycle and proliferation markers (Mib-1, p53, p16, Cyclin D1) and PcG proteins (BMI-1, EZH2, MEL-18) was examined and correlated to clinical data. Statistical analysis was performed using the Mann-Whitney U, Kaplan Meier and Cox regression analysis where appropriate.
Results: P53, p16, Mib-1, Cyclin D1 and EZH2 expression was increased in ACC compared to normal tissue (p<0.001). P16 was up-regulated in presence of BMI-1. Cyclin D1 expression was lower (p=0.02) in tumours with metastases. P16 expression was significantly higher (p=0.05) in tumours that recurred. With Cox regression analysis patients with long term survival could be identified, either by absence of Cyclin D1 expression, or by both low EZH2 and p16 expression.
Conclusion: Expression of the two PcG complexes is deregulated in ACC. Negative regulation of p16 is not associated with expression of BMI-1. An algorithm based on Cyclin D1, EZH2 and p16 expression can possibly be used in the future to define patient subpopulations with favourable clinical outcome.