Epithelioid trophoblastic tumor presenting as a lung mass without uterine involvement: Pitfalls in morphology and immunohistochemistry.

Epithelioid trophoblastic tumor (ETT) presenting as a lung mass without uterine involvement is extremely rare. We report a case of ETT with isolated pulmonary involvement in a 30-year-old female. The tumor's morphological and immunohistochemical features, including p40 expression, may mimic primary squamous cell carcinoma (SCC). Therefore, when diagnosing lung SCC in young women, thorough review of clinical history and the use of immunohistochemical analysis are essential to exclude other potential diagnoses.