FEN1 and cancer: The quantitative proteome of a human cancer cell line47 (nuclear volume48 of ~1472 μm3) shows the contrary of this requirement; FEN1 (1.40 × 105 copies/cell; ~158 nM) is considerably more abundant than Polδ p125 (1.96 × 104 copies/cell; ~22 nM) or Lig1 (2.56 × 104 copies/cell; ~29 nM).