ARID1A and neoplasm: Thus, the finding that PCNA positivity was much higher than Ki67 positivity in the Arid1aLKO mice reflects that the more DNA replication and mitotic activity in G0/S phases, not cell division, occurs in HCC cells in the absence of Arid1a. Genotypes of these HCC samples, including tumor cells harvested by LCM, showed that these tumors were mainly composed of Arid1a-deficient cells (Fig 2E).