High-grade serous ovarian cancer (HGSC) is among the most lethal forms of cancer in women. Excessive genomic rearrangements, which are expected to create fusion oncogenes, are the hallmark of this cancer. Here we report a cancer-specific gene fusion between BCAM, a membrane adhesion molecule, and AKT2, a key kinase in the PI3K signaling pathway. This fusion is present in 7% of the 60 patient cancers tested, a significant frequency considering the highly heterogeneous nature of this malignancy. Further, we provide direct evidence that BCAM-AKT2 is translated into an in-frame fusion protein in the patient's tumor. The resulting AKT2 fusion kinase is membrane-associated, constitutively phosphorylated, and activated as a functional kinase in cells. Unlike endogenous AKT2, whose activity is tightly regulated by external stimuli, BCAM-AKT2 escapes the regulation from external stimuli. Moreover, a BCAM-AKT2 fusion gene generated via chromosomal translocation using the CRISPR/Cas9 system leads to focus formation in both OVCAR8 and HEK-293T cell lines, suggesting that BCAM-AKT2 is oncogenic. Together, the results indicate that BCAM-AKT2 expression is a new mechanism of AKT2 kinase activation in HGSC. BCAM-AKT2 is the only fusion gene in HGSC that is proven to translate an aberrant yet functional kinase fusion protein with oncogenic properties. This recurrent genomic alteration is a potential therapeutic target and marker of a clinically relevant subtype for tailored therapy of HGSC.cancer-specific fusion gene | high-grade serous ovarian cancer | AKT2 | BCAM | fusion kinase O varian cancer is responsible for the death of ∼140,200 women yearly, and 70% of these deaths are due to the high-grade serous ovarian cancer (HGSC) subtype (1), which is typically detected only after it has metastasized. Genomic characterization of HGSC tumors shows that TP53 mutations are present in 96% and BRCA1/2 in 22% of HGSC (2). These mutations are thought to occur early in pathogenesis (3) and promote genomic instability, thus giving rise to the high degree of heterogeneity and genomic rearrangements that are characteristic of these cancers. The characteristic genome rearrangements in HGSC imply that recombination events such as gene fusions should be common. Moreover, if the activity of a fusion gene represents a common oncogenic mechanism, the same fusion gene is likely to occur in many patients.Recurrent fusion genes are important for understanding cancer mechanisms and developing useful clinical biomarkers and anticancer therapies. For instance, the BCR-ABL fusion gene in chronic myeloid leukemia is known to initiate oncogenesis through formation of a misregulated BCR-ABL fusion kinase. The BCR-ABL fusion gene is also a clinical biomarker of high diagnostic and prognostic utility in chronic myeloid leukemia. In addition, this fusion protein serves as a therapeutic target for the successful drug imatinib (4). In solid human tumors, fusion genes such as the TMPRSS2-ERG fusion in prostate cancer (5), FGFR-TACC in glioblastoma (6), and DNAJB1...