Genomic Analysis of Low-Grade Serous Ovarian Cancer: Clinical and Biological Insights

Low-grade serous ovarian cancer (LGSOC) is a rare and clinically unique epithelial ovarian cancer (EOC) subtype that occurs in younger women, presents in an indolent but progressively persistent fashion, and is relatively resistant to conventional chemotherapy. LGSOC has a stable genome and low mutational load (median mutational burden <1 mutation/Mb), very different from high-grade serous ovarian cancer, which is characterized by high genomic instability, with nearly universal TP53 mutation. Its pathogenesis is strongly associated with activation of the MAPK pathway. Mutually exclusive mutations in KRAS, BRAF, or NRAS are detected in approximately 50-60% of LGSOC cases and often arise early in the development of serous borderline tumors. Further features, such as NF1 loss, MAP2K1 mutations, ERBB2 activation, and frequent copy number changes (including CDKN2A/2B deletion and 1p/1q imbalances), add to tumor heterogeneity and evolution. In addition to genomics, transcriptional and epigenomic profiling uncovers a high prevalence of estrogen receptor signaling, epithelial-mesenchymal transition-related pathways, and promoter hypermethylation of tumor suppressors (CDH1 and RASSF1A). Additionally, loss of microRNAs (e.g., miR-7) and deregulated chromatin regulators further promote tumor cell survival and resistance to apoptosis. These layers highlight that, however "silent" the enzymatic activity has been described to be, the biology of LGSOC is driven by a complex set of molecular and regulatory mechanisms. Clinically, identification of the dependency on MAPK has guided targeted therapies. The cooperative GOG 281/LOGS trial showed that trametinib, an MEK inhibitor (MEKi), was significantly more effective than standard-of-care options (including chemotherapy or hormonal therapy) in increasing progression-free survival (median PFS 13.0 months vs. 7.2 months; hazard ratio 0.48, p < 0.001). Nevertheless, while MEKi have demonstrated clinical benefit, the emergence of resistance (frequently associated with activation of the NOTCH pathway) highlights the need for rational combination strategies. The therapeutic horizon extends with hormonal treatment targeting ER/PR and exploratory approaches using epigenetic agents, BCL-2 inhibition, and DDR-targeted therapy. In summary, LGSOC is biologically and clinically distinct from HGSOC and from other subtypes of ovarian cancer. Genomic and multi-omic profiling have revealed actionable vulnerabilities and precision oncology approaches. The advent of biomarker-directed trials, molecular subtyping incorporation, and innovative computational strategies is likely to gradually ameliorate therapy selection and, thereby, finally improve long-term outcomes for patients with this complex disease.