Choriocarcinoma Histologically Mimicking Epithelioid Trophoblastic Tumor – A Diagnostic Pitfall in Gestational Trophoblastic Neoplasia

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Abstract
Background: Histopathological diagnosis can be challenging because epithelioid trophoblastic tumor (ETT) may closely mimic choriocarcinoma, particularly due to overlapping cytologic and architectural features of intermediate trophoblasts. Therefore, immunohistochemical studies are essential for accurate classification of GTN subtypes. Case Illustration: A 27-year-old woman, para 4 abortion 1, with a history of two curettage procedures for partial hydatidiform mole, presented with persistent post-curettage vaginal bleeding for five months and was admitted to the emergency department with severe anemia. Serial β-hCG monitoring demonstrated a significant rise, raising suspicion for GTN. Ultrasonography revealed a vesicular pattern, while additional investigations showed no evidence of metastasis. Based on a FIGO score < 7, the patient was classified as low-risk GTN. The patient declined chemotherapy and opted for total hysterectomy with bilateral salpingectomy. Intraoperative gross examination revealed an irregular, friable, and necrotic uterine mass consistent with GTN. Initial histopathological evaluation suggested epithelioid trophoblastic tumor; however, further immunohistochemical analysis demonstrated negative p63 expression, high Ki-67 index, and positive β-hCG staining, findings more consistent with choriocarcinoma. Discussion: This case highlights the importance of post-molar β-hCG surveillance as a cornerstone for early GTN diagnosis. The biological differences between ETT and choriocarcinoma have significant therapeutic implications, given the poorer chemotherapy response observed in ETT. Overlapping histopathological features emphasizes that diagnosis cannot rely solely on morphology but requires integration of clinical data, disease latency, β-hCG levels, and an appropriate immunohistochemical panel, particularly p63. Conclusion: Delayed post-molar β-hCG monitoring may lead to GTN progression and increased morbidity. Immunohistochemical examination plays a crucial role in differentiating ETT from choriocarcinoma to ensure accurate diagnosis and appropriate management.

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