Abstract Mucinous ovarian tumor represent a distinct histotype of epithelial ovarian cancer and is thought to begin as a mucinous adenoma that progresses in a slow stepwise fashion. Dedifferentiated mucinous ovarian carcinoma is a rare type of carcinoma with a few reports and a progressive and poor prognosis. While the molecular genetic features of ovarian mucinous carcinoma is now well known, the pathogenesis of dedifferentiated mucinous carcinoma is largely unknown. In order to comprehensively analyse somatic mutations in dedifferentiated mucinous carcinoma, we applied exome sequencing to the DNA of a sample of affinity-purified, dedifferentiated mucinous carcinoma. Through comparative analyses of normal cells from the same patient, we identified several genes that were mutated in this tumor. P53, which encodes a well-known tumor suppressor protein, and KRAS, which encodes a well-known oncoprotein, had previously been implicated in ovarian mucinous carcinoma. The other mutated genes were previously unknown to be involved in mucinous carcinoma. CEP170 encodes a microtubule-binding protein that controls the targeting of the kinesin-13 depolymerase protein to the mitotic spindle, and kinesin-13 family influence the dynamics of microtubule growth and shrinkage. CEP170 gene mutation may be related to inability of a cell division properly. CEP170 mutations were identified with a prevalence of 33.3% in dedifferentiated mucinous ovarian carcinoma. Currently, CEP170 gene knock down assay and engineered expression of CEP170 assay in ovarian mucinous carcinoma is being performed whether morphologic change is observed. In summary, CEP170 may be one of the responsible gene in carcinogenesis of differentiated mucinous carcinoma. Citation Format: Kaori Sanuki, Kentaro Nakayama, Kohei Nakamura, Masako Ishikawa, Tomoka Ishibashi, Hitomi Yamashita, Ruriko Ono, Toshiko Minamoto, Kosuke Yoshihara, Satoru Kyo. Exome sequencing in dedifferentiated ovarian mucinous carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3383. doi:10.1158/1538-7445.AM2017-3383