RB1 and breast cancer: Cytogenetic studies in BRCA1+ familial breast cancer showed the losses of 2q, 4p, 4q, 5q, and 12q[8]; analysis of a breast cancer-derived cell line HCC1937 showed aneuploidy, loss of p53 and PTEN, and loss of heterozygosity (LOH) at multiple loci[9]; analysis in BRCA1+ basal-like breast cancer identified the losses of the regions containing RB1, INPP4B, RAD17, RAD50, and RAP80[10], and large-scale chromosomal breakage, copy number loss and LOH[11,12].