These cases indicate that a lack of elevated testicular tumor markers such as LDH, β-hCG, and AFP does not exclude the existence of a primary testicular mucinous tumor, while increased CA19-9 and CEA levels might provide an early indication of a testicular mucinous tumor, especially mucinous adenocarcinoma or mucinous borderline tumor. The gene discussed is AFP; the disease is mucinous neoplasm.