Hazama Y, et al. – Given that the frequency of ovarian clear cell carcinoma (CCC) is twice as high in Japan vs the United States and Europe with a poor prognosis due to chemoresistance, the authors assessed the cell cyle—one of the mechanisms of chemoresistance—to detect the informative markers and improve the strategy of chemotherapy for CCC. To this end, they performed immunohistochemical staining using the antibodies of cell cycle-related proteins such as Ki-67, Cdt1, MCM7, and geminin in ovarian malignant tumors. Each of the 29 samples of CCC and high-grade serous carcinoma (HGSC) were identified as essential to reveal the significant differences in immunostaining and prognosis. As per findings, the cancer cells of CCC and HGSC exist in the G1 phase and S, G2, and M phases, respectively. The differences in cell cycle of CCC might partly explain chemotherapy resistance.