FEN1 and breast carcinoma: The Northern dot blotting results showed that FEN1 expression levels in breast cancer cell lines, MDA-MB-4355 and MDA-MB-231, increased significantly (by more than 8 folds) after the treatment with DNA-damaging agents, such as camptothecin, cytochalasin D, MMC, and gamma irradiation (Figure 5A and B).