KRAS and clear cell adenocarcinoma: Low-grade ones, including serous carcinoma, mucinous, endometrioid, and clear cell carcinomas, likely to arise stepwise in an adenoma (borderline tumor) carcinoma sequence from typical to micropapillary borderline tumors to low-grade invasive serous carcinoma, with a lower rate of progression and be caused by mutation in different genes including KRAS, BRAF, PTEN, and beta-catenin, and KRAS or BRAF mutations lead to the effective activation of the MAPK signaling in low-grade serous carcinoma cells (14).