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Introduction/Background The role of molecular classification in patients with low/intermediate risk endometrial cancer (EC) is uncertain. Higher precision in diagnostics will inform the unsettled debate on optimal adjuvant treatment. Methodology We retrospectively included patients referred to The Norwegian Radium Hospital, Oslo, Norway (2006–2017). Patients with low/intermediate risk EC were molecularly classified as pathogenic polymerase epsilon (POLE)-mutated, mismatch repair deficient (MMRd), p53 abnormal, or no specific molecular profile (NSMP). The main outcome was time to recurrence (TTR) and cancer-specific survival (CSS) within the molecular subgroups. We also studied patterns of recurrence in molecular groups. Results Of 626 patients, 610 could be molecularly classified and only 24 received adjuvant treatment. Molecular subgroup distribution was: 57 patients (9%) with POLE-mutated tumors, 202 (33%) with MMRd tumors, 34 (6%) with p53 abnormal tumors, and 317 (52%) with NSMP tumors. After a median follow-up time of 8.9 years (95% confidence interval (CI): 6.2–12.6 years), there was a statistically significant difference in TTR (pConclusion Large differences in prognosis and localization of recurrence by molecular groups demand a higher precision in diagnostics, also in patients with low and intermediate risk EC. Tailored adjuvant treatment strategies need to consider systemic treatment for patients with p53 abnormal tumors and de-escalation of treatment in patients with POLE mutated tumors. Disclosures KL: Receipt of grants/research supports: GSK, research funding paid to Institution; Receipt of honoraria or consultation fees: Advisory board fees: Astra Zeneca, Nycode, GSK, Eisa GK: Stockholder: Novo Nordic
Lindemann et al. (Fri,) studied this question.