Introduction/Background High-grade endometrial carcinomas, such as FIGO grade 3 endometrioid carcinoma (EC3) and serous carcinoma (SEC), pose diagnostic challenges due to overlapping and ambiguous features. The significance of clinicopathologic characteristics and prognosis of ambiguous cases remain unclear, adversely affecting the provision of individualised patient counselling and management.

Methodology This analysis of 129 consecutive cases of EC3 and SEC at Soroka University Medical Center (2006–2022) compares clinicopathologic characteristics and prognosis in definite and ambiguous EC3 and SEC. All pathological slides were revised and reclassified as definite or ambiguous for EC3 and SEC and prognostic data was extracted retrospectively from medical records. Survival, progression-free survival, and associations between tumour histologic type and clinicopathologic factors were analysed.

Results Definite SEC displayed higher mortality compared to definite EC3 (68.2% vs. 41.4%, p=0.023) and a non-significant trend towards diminished 5-year survival (48.3% vs 60.1%, p=0.096). Ambiguous SEC also showed higher mortality compared to ambiguous EC3 (68.8% vs. 37.5%, p=0.020) and a non-significant trend towards reduced 5-year survival (30.5% vs 55.1%, p=0.098). Overall, ambiguous cases displayed behavior that fell between the two definite groups, with a mortality rate exceeding that of definite EC3 but favourable to that of definite SEC (p=0.024). Other variables showed a similar trend, including lymph node metastases (p=0.013) and omental involvement (p=0.002). No significant differences were observed in 5-year progression-free survival between all the subpopulations in the study (p=0.288).

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Abstract #346 Figure 1

Mortality rate (A) and Clinicopathologic factors (B): Definite FIGO Grade 3 Endometrioid Carcinoma (EC3), Serous Carcinoma (SEC), and Ambiguous Cases of Endometrial Cancer.

Conclusion This study highlights the importance of accurate histological classification in high-grade endometrial carcinoma subtypes. Ambiguous cases constitute a distinct intermediate group with clinicopathologic features more aggressive than definite EC3 but less than definite SEC, potentially influencing counselling and management of these patients. Further research into the underlying mechanisms and prognostic implications is imperative for developing personalised therapeutic approaches and improving patient outcomes.

Disclosures The authors have nothing to declare.