High nuclear FEN1 expression in the DCIS component of the mixed cohort was associated with higher nuclear grade (p < 0.001), DCIS comedo necrosis (p < 0.001) and negative ER status (p = 0.002), while FEN1 cytoplasmic expression did not reveal any significant association in statistical analysis. This evidence concerns the gene FEN1 and ductal breast carcinoma in situ.