RB1 and ductal breast carcinoma in situ: In the breast, short telomeres and widespread genomic instability can first be observed in premalignant lesions such as ductal carcinoma in situ (DCIS) [20,22], a stage where the p53 and Rb pathways are usually inactivated [63,64,65], suggesting that these lesions develop from cells expressing insufficient telomerase for telomere length maintenance.