Promoter methylation of p16^INK4a, RASSF1A, and DAPK is frequent in salivary adenoid cystic carcinoma

BACKGROUND. Promoter methylation is a common mechanism of inactivation of tumor suppressor genes in multiple tumor types. However, little is known about its role in the development of adenoid cystic carcinoma of the salivary gland (ACC). In the current study, the authors investigated whether promoter methylation is common in ACC and whether it may influence ACC development. METHODS. The promoter methylation status of the genes p16^INK4a, RASSF1A, DAPK, and MGMT, which are important in cell growth regulation, apoptosis, and DNA repair, was determined in tissue sections of tumor samples from 60 patients with ACC using methylation-specific polymerase chain reaction. The association between methylation status and patients' clinical and pathologic characteristics were assessed. RESULTS. Of the 60 tumors, DNA methylation of the p16^INK4a promoter was detected in 28 tumors (47%); the respective values DNA methylation of the RASSF1A, DAPK, and MGMT promoters were 25 tumors (42%), 16 tumors (27%), and 4 tumors (7%), respectively. Forty-six tumors (77%) had DNA methylation in ≥ 1 of the 4 promoters, 20 tumors (33%) had DNA methylation in ≥ 2 promoters, 6 tumors (10%) had DNA methylation in ≥ 3 promoters, and 1 tumor (2%) had DNA methylation in all 4 promoters. RASSF1A promoter methylation was more frequent in high-grade tumors than in low-grade tumors (P = 0.009), in advanced-stage tumors (P = 0.008), and in tumors with metastasis (P = 0.005). CONCLUSIONS. Promoter methylation of p16 ^INK4a, RASSF1A, and DAPK was common in ACC, and it is possible that such methylation may influence the development of ACC. The high frequency of RASSF1A promoter methylation in high-grade tumors and in tumors with metastasis suggested a role for this gene in the progression of ACC.