- Histomorphology consistent with carcinoma. Hepatoid morphology is allowed. - Positive IHC for AFP in ≥ 1% of tumor cells. - Absence of morphological patterns characteristic of yolk sac tumor but inconsistent with carcinoma. These include a reticular/microcystic pattern, Schiller-Duval bodies, and loose myxoid stroma. The gene discussed is AFP; the disease is neoplasm.