Cyclin E1 overexpression identifies a therapeutically relevant poor prognostic patient subgroup in high-grade serous ovarian cancer.

Cyclin-E1 protein overexpression, including through CCNE1 gene amplification, is recognized as a poor prognostic factor in high-grade serous ovarian cancer (HGSOC) and is a promising predictive marker for investigational therapies targeting cell-cycle checkpoints. However, the demonstration of its clinical utility remains elusive due to inconsistent definitions of protein overexpression and gene amplification. This study characterizes Cyclin-E1 overexpression and CCNE1 amplification prevalence and prognostic value in HGSOC using both original and public clinical cohorts. Fifty-nine percent of tumors overexpressed Cyclin-E1, more than half of which had no evidence of CCNE1 gene amplification. The prevalence of CCNE1 amplification varied across studies and was higher in interventional studies. Patients with Cyclin-E1 positive tumors had poorer outcomes after adjuvant therapy. Platinum-based chemotherapy increased Cyclin-E1 expression. These patients were less likely to benefit from PARP inhibitors (75% are BRCA-wildtype) or mirvetuximab-soravtansine (67% were not FRα-high), highlighting a distinct patient population in need of novel therapies.