CCND1 and head and neck squamous cell carcinoma: It has previously been shown that mutations in CDKN2A gene are evident in over 75% of HNSCC specimens studied.24,25 In addition, Leemans et al. reported an amplified expression of up to 80% of cyclin D1 in HNSCC.22 These findings suggest that both inactivation of CDKN2A and overexpression of cyclin D1 may be necessary to produce aberrant cell-cycle progression through cyclin-dependent kinases 4 and 6.