PCNA and breast cancer: A close examination reveals that many breast cancer susceptibility genes including BRCA1, BRCA2, P53, PCNA [46], FOXA1 [47] and STK6 [48] from recent individual studies and breast cancer biomarker genes such as ERBB2, FGFR2, M3K1, and PTEN [49,50], have all been found in this list.