886 Malignant Uterine PEComa – a Case Series

Introduction/Background Perivascular epithelioid cell tumours (PEComas) are rare mesenchymal tumours identified by their distinct histology and immunophenotype. Majority of described PEComas occurred in the female gynaecological tract, mostly arising in the uterine corpus, of those around 45 classified as malignant. Methodology Clinical, imaging, histopathological, treatment and follow-up data of malignant uterine PEComa (as per modified criteria by Bennett) treated between 2018 and 2023 was retrospectively analysed. Results 3 cases were identified, aged 43 (case 1), 65 (case 2) and 75 years (case 3). All presented with clinical symptoms. On imaging, all tumours were well circumscribed, in case 3 and 2 they exhibited intracavitary submucous growth. Cases 3 and 2 were diagnosed by histopathological examination of specimens obtained by curettage or biopsy and subsequently underwent hysterectomy with adnexectomy and pelvic sentinel node biopsy (case 2). Case 1 underwent enucleation of presumed myoma by Pfannenstiel laparotomy, resulting in R1 resection. Sizes of the tumours were 5cm, 9cm and 7cm for cases 1–3, respectively. Cervical stromal invasion was present in case 2, other two tumours were confined to the uterus. Most commonly expressed IHC markers were HMB45, desmin, caldesmon. Mutation in TSC1 was detected in case 2, NGS profiling has not been done in others. None of the patients received adjuvant treatment. Cases 1 and 2 were without evidence of disease at 22 and 7 months, respectively. Patient in case 3 recurred at 9 months and underwent two lines of mTOR inhibitor therapy but succumbed to local and peritoneal spread at 15 months. Conclusion Our series contributes 3 cases of malignant uterine PEComa to existing literature. Described patients vary by age, clinical and imaging features, treatment and outcomes. This is consistent with the previously described unpredictable nature of these tumors. Disclosures None for all authors.