For instance, bialleic loss of RB1 and mutations has been recognized in retinoblastoma lesions and lung cancers.45, 46 However, in prostate carcinoma, RB1 gene is inactivated by a deletion within its promoter region.47 Furthermore, CpG island methylation in the promoter of RB1 may result in the inactivation of this gene, leading to oncogenesis.48 As there are more CpG islands in bidirectional promoters than in non-bidirectional promoters. This evidence concerns the gene RB1 and lung cancer.