Epithelioid trophoblastic tumor: a misdiagnosis-prone tumor with immune checkpoint expression and immunotherapeutic implications

Background/Objectives Epithelioid trophoblastic tumor (ETT) is the rarest form of gestational trophoblastic neoplasia and is highly prone to misdiagnosis due to its morphological overlap with squamous cell carcinoma and epithelioid leiomyosarcoma. It is also relatively chemoresistant, and effective therapies for recurrent or metastatic disease remain lacking. Methods We retrospectively analyzed five ETT cases, integrating clinicopathological review, immunohistochemistry for diagnostic markers (GATA-3, p63, p40, p16) and immune checkpoints (PD-L1, PD-L2, B7-H3, VISTA), and multiplex immunofluorescence to resolve spatial co-expression. Results Four cases were initially misdiagnosed. p40 was focally positive in all five ETT cases, with diffuse strong positivity in SCC controls, highlighting a potential diagnostic pitfall. PD-L1 CPS ranged from 10 to 60; PD-L2 and B7-H3 were predominantly expressed on tumor cells, with B7-H3 showing the highest positivity. VISTA was largely confined to CD3+ immune cells, with only rare tumor-cell expression. Multiplex immunofluorescence revealed frequent co-expression of B7-H3, PD-L1, and PD-L2 on GATA-3+ tumor cells, with triple-positive cells ranging from 5% to 35% across cases, indicating co-expression of multiple immune checkpoint molecules.A Conclusions These findings refine diagnostic awareness and provide a pathological rationale for immunotherapy in ETT. The immune checkpoint co-expression pattern supports further evaluation of combination immunotherapeutic strategies in this rare, chemoresistant malignancy.