For example, FRA3B is the most frequent fragile locus in lymphocytes, but does not seem to be fragile in epithelial cell lines [24, 26], possibly due to the plasticity of replication programs in different cell lineages or because of a putative “housekeeping” role of FHIT. The second most fragile site, FRA16D, is very frequently affected in epithelial breast cancer cell lines (20–25 %), but only occasionally in colon epithelial cells (~5 %). This evidence concerns the gene FHIT and breast cancer.