RB1 and neoplasm: Importantly, methylation of non-histone substrates such as tumour protein 53 (p53), heat shock proteins 70 or 90 (HSP70 or HSP90), nuclear factor kappa B (NF-κB) and Retinoblastoma 1 (RB1) has been implicated in modulating DNA damage repair, apoptosis, and survival signalling in tumours [41,45].