APC and neoplasm: To broaden the knowledge of epigenetic events in parathyroid tumour development, we sought to determine the levels of promoter methylation of four tumour suppressor genes; APC (adenomatous polyposis coli), p16INK4A, RASSF1A (Ras association domain family protein 1) and RAR-β (Retinoic acid receptor-beta), all known to be widely hypermethylated in various human cancers as well as exhibiting potential as parathyroid tumour suppressor genes.