EP20.21: Atypical epithelioid trophoblastic lesion: a case report and review of the literature

In 2020, the WHO introduced Atypical Placental Site Nodule (APSN) into the new classification of female genital tract tumours, describing it as an intermediate lesion between placental site nodule (PSN) and epithelioid trophoblastic tumour (ETT). Unlike APSN which is typically a nodule, we present a case of a post-Caesarean Section (CS) cyst and fistula formation with intermediate behaviour between PSN and ETT. This type of lesion has earlier been described as “atypical epithelioid trophoblastic lesion”. We aim to review similar cases in the literature to gather data on clinic, sonographic and histopathological characteristics. We conducted a search on PubMed and Web of Science databases. Given the novelty of the term atypical epithelioid trophoblastic lesion and its lack of validation, we broadened our search to the term 'APSN' including similar cases with unique clinicopathologic features, specifically those involving cyst and fistula formation after CS. Two reviewers independently screened articles and extracted relevant data. We describe a case of atypical epithelioid trophoblastic lesion presenting as a cystic lesion anterior to a Caesarean scar niche. We found 8 cases similar in literature. All presented with a cyst and/or fistula that occurred several months, or even years, after CS. Symptoms were vaginal bleeding, abdominal pain, hematuria, amenorrhea and urinary frequency. Ki-67 proliferation indices exceeded 12% in 4/8 (50%) cases. Necrosis or mitotic figures were not observed in 7/8 (87.5%) cases. No case displayed signs of recurrence during follow-up (range: 1-12 months). There are only 8 similar cases in literature that displays similar sonographic and histopathological features to the case report we presented. Further molecular studies focusing on the gene signature and data from gestational trophoblastic disease registries could contribute to a better understanding of the origin of this specific intermediate lesion.