The finding that SSA-TI can occur before S phase, particularly when the target site has a DSB, implies that precision gene targeting is feasible in cells with a limited number of divisions such as normal somatic cells, in cells that are deficient in HR (e.g., BRCA1/2-defective cancers, as demonstrated in this study), and possibly in cells that have lost their mitotic potential due to differentiation (e.g., neurons or cardiac muscle cells). This evidence concerns the gene BRCA1 and cancer.