CHAPTER 6 136 ABSTRACT Objective The prognostic relevance of hormonal biomarkers in endometrial cancer (EC) has been well-established. A refined three-tiered risk model for estrogen receptor (ER)/progesterone receptor (PR) expression was shown to improve prognostication. This has not been evaluated in relation to the molecular subgroups. This study aimed to evaluate the ER/PR expression within the molecular subgroups in EC. Methods A retrospective multicenter cohort study was performed and data from the European Network for Individualized Treatment centers and Vancouver, Canada were used. ER/PR immunohistochemical expression was grouped as: ER/PR 0-10%, 20-80% or 90-100%. Molecular subgroups were determined with full next-generation sequencing or combined with immunohistochemistry: POLEmut, mismatch repair deficient (MMRd), p53mut and nospecific molecular profile (NSMP). Results A total of 739 patients were included (median follow-up 5.0 years). Tumors were classified as POLEmut in 9.1% (N=67), MMRd in 27.6% (N=204), p53mut in 20.8% (N=154) and NSMP in 42.5% (N=314). Among all molecular subgroups, patients with ER/PR 90-100% expression revealed the best disease-specific survival (DSS). Within p53mut, PR 90-100% expression showed a 5-year DSS of 100.0%. ER expression is prognostic more relevant in MMRd and NSMP tumors while PR expression in p53mut and NSMP tumors. Across all molecular subgroups, PR 0-10%, p53mut, lympho-vascular space invasion and FIGO stage III-IV remained independent prognostic for reduced DSS Whereas PR 90-100% and POLEmut remained independent prognostic for improved DSS. Conclusion We demonstrated that ER/PR expression remain prognostically relevant within the molecular subgroups, and that a three-tiered cutoff refines prognostication. These data support incorporating routine evaluation of ER/PR expression in clinical practice.
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