RASSF1 and tumor of parathyroid gland: However, no statistical correlation between increased RASSF1A promoter methylation density and over-expressed cyclin D1 levels were seen (data not shown), suggesting that RASSF1A hypermethylation at least in part might contribute to excessive parathyroid tumour growth by other means than cyclin D1 accumulation, for example through its role as a regulator of apoptosis and mitotic arrest [19].