FEN1 and neoplasm: Cases with H.N/ H.C FEN1 expression were more likely expressed in DCIS with an aggressive behaviour: larger tumour size (p = 0.012), high nuclear grade (p = 0.003), comedo necrosis (p < 0.001), negative ER (p < 0.001), negative PR (p < 0.001), higher proliferation index (p < 0.001) and triple-negative subtype (p < 0.001) (Table 3).