Background: Somatic alterations in genes in the PTEN-PI3K-AKT-mTOR pathway are common in ovarian cancer. The frequency of pathway alterations varies among histologic subtypes. The PI3K/AKT pathway has also been linked to ovarian cancer platinum resistance. Methods: 379 patients with ovarian or fallopian tube cancer were enrolled in an IRB-approved protocol at Dana-Farber Cancer Institute and provided informed consent. Formalin-fixed tumor tissue underwent next-generation sequencing (NGS) of 300 cancer-associated genes (OncoPanel test), without germline analysis. Single-nucleotide variants (SNVs) and insertions/deletions in the targeted cancer genes were identified, as well as putative copy number variations and structural rearrangements. We determined the frequency of alterations in 10 genes in the PTEN-PI3K-AKT-mTOR pathway in the panel (AKT1, AKT2, AKT3, MTOR, PIK3CA, PIK3C2B, PIK3R1, PTEN, TSC1, and TSC2). Alterations in the entire cohort and across histologic subtypes were summarized with descriptive statistics.Results: About one-third of the ovarian cancer patients harbored aberrations in at least one of ten selected genes in the PTEN-PI3K-AKT-mTOR pathway. PIK3CA alterations were the most common (12%), primarily SNVs corresponding to known hotspot mutations. PTEN alterations were identified in ~10% of patients, including 27 SNVs and five 2-copy deletions. AKT2 amplifications were present in ~2%. Other alterations included deletions and truncating mutations in PIK3R1 and missense mutations in mTOR, TSC1, TSC2, and PIK3C2B. 70% of cases harbored a TP53 missense or nonsense mutation, and PTEN-PI3K-AKT-mTOR pathway alterations occurred both in the TP53 mutant and wildtype groups. Conclusions: We describe somatic mutations and copy number variations in the PTEN-PI3K-AKT-mTOR pathway in a large cohort of ovarian cancer patients. This study further demonstrates the feasibility of NGS of cancer-associated genes in formalin-fixed tissues. Preliminary correlations of genetics with survival and treatment response are being investigated. These data suggest potentially clinically actionable alterations and may inform the use of inhibitors of PI3K/AKT signaling in ovarian cancer.