PCNA1 (Proliferating Cell Nuclear Antigen) is an auxiliary protein for DNA polymerase that is highly expressed during the S phase of the cell cycle and is widely used as an index of the proliferative cell activity in cancer tissues and plant cells (Strzalka and Ziemienowicz, 2011; Yokoyama et al., 2016). The gene discussed is PCNA; the disease is cancer.