FEN1 and ductal breast carcinoma in situ: High nuclear FEN1 expression was associated with aggressive clinicopathological variables in the pure DCIS cohort including larger tumour size (p = 0.008), high nuclear grade (p < 0.001), comedo type of necrosis (p < 0.001), negative hormonal status (p < 0.001), higher proliferation index (p < 0.001) and triple-negative tumours (p < 0.001) (Table 1).