Genetic variation in TERT, TRF1, TRF2, POT1, TEP, TNKS1, TNKS2, TP53, ATRX and DAXX [17–24] and aberrant promoter methylation of TERT, WRN, POT1, RAD50 and TP53 [25–28] have been reported to contribute to the dysregulation of telomere length and telomerase activity in breast cancer. This evidence concerns the gene TERF1 and breast cancer.