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Extragonadal GCT — SCE Medical Oncology MCQ

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HardCancer of Unknown PrimaryExtragonadal GCTSCE Medical Oncology

A 65-year-old man presents with poorly differentiated carcinoma in a midline location (mediastinum). He is a young-appearing non-smoker. AFP is mildly elevated. HCG is normal. Immunohistochemistry shows OCT4+ and SALL4+. What is the diagnosis?

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Correct answer: B — Primary mediastinal non-seminomatous germ-cell tumour

A midline mediastinal mass with OCT4 and SALL4 expression plus AFP elevation is classified as a primary mediastinal non-seminomatous germ-cell tumour. Primary mediastinal seminoma with syncytiotrophoblastic differentiation: AFP elevation argues against pure seminoma. Mediastinal yolk-sac tumour arising within a mixed germ-cell tumour: this is a possible component, but the requested overarching classification is non-seminomatous GCT. Metastatic hepatoid adenocarcinoma with aberrant germ-cell marker expression: the midline setting and OCT4/SALL4 profile favour germ-cell origin. NUT midline carcinoma with secondary serum AFP elevation: NUT carcinoma requires NUTM1 evidence and does not fit the germ-cell immunophenotype.

Reference: EAU testicular-cancer guideline: diagnostic evaluation and staging (2026 limited update): https://uroweb.org/guidelines/testicular-cancer/chapter/diagnostic-evaluation; NICE CSG2 urological cancer service guidance (Current NICE service guidance, accessed July 2026): https://www.nice.org.uk/guidance/csg2