Ovarian serous cystadenocarcinoma (OSC), the leading common subtype of epithelial ovarian cancers (EOC) accounting for 90% of OC, harbors overall genetic alterations of PIK3CA (29%), PIK3R1 (5%), PIK3R2 (9%), AKT1 (5%), AKT2 (8%) and PTEN (7%, Table 1) besides the mutant p53 in high-grade OSC (HGOSC), germline BRCA1 and BRCA2 mutations. Here, PIK3R1 is linked to ovarian serous cystadenocarcinoma.