Sequencing analysis of all 27 exons of the RB1 gene in those neoplasms with LOH at the RB1 locus showed a low rate (5–12%) of inactivating mutations, suggesting the location of another tumour suppressor gene at 13q14 or the existence of another RB1 silencing mechanism, such as promoter hypermethylation (Ishikawa et al, 1991; Ichimura et al, 1996; Tsuzuki et al, 1996; Ueki et al, 1996). The gene discussed is RB1; the disease is neoplasm.